Not only at the funeral service, but also any time she is visiting his grave, a woman in mourning is shown wearing a black dress and/or a black hat with a veil. Usually this is the widow of the deceased, but it can be other close female relatives as well, such as his mother, sister, or daughter. Spear Counterpart is a man wearing a black armband to show mourning, since men wear black suits in other contexts as well.
According to That Other Wiki, black clothing and veils were colloquially called "widow's weeds" during the Victorian era, from the Old English word "waed," meaning "garment."
Not to be confused with Black Widow. Or a widow carrying THOSE kind of weeds. Compare Woman in Black, but this is more specific and less vampy.
In other cultures, the traditional color of mourning may be other than black.
Josie and the Pussycats: In a "what if" Fantasy Sequence, Melody is persuading Alan M to let Josie help out more, instead of playing macho and doing it all himself. She describes a future in which Alan M and Josie are married, and Alan M works himself into an early grave trying to support her. "Before long, Josie is buying a dress she hadn't planned for." Josie is pictured in a black veil, shopping for the dress to wear to his funeral, while a sales clerk observes, "Basic black? We've been selling a lot of those lately."
In Jaws, a grieving mother angrily confronts an official because he didn't close the beach, and now her son is dead. She is wearing a black hat with a veil.
In The Great Train Robbery, Miriam wears this as a part of the robbers' scheme to persuade the conductor that her supposedly deceased husband's coffin may travel inside the train's secure vault.
Subverted in Thunderball. While James Bond is watching the funeral of SPECTRE agent Colonel Jacques Bouvar, he sees that Bouvar's widow is wearing a black dress, hat and veil. Then he realizes that the widow isn't a woman at all...but a man, baby!
Scarlett O'Hara ends up burying two husbands in Gone with the Wind and wears mourning on both occasions.
In The Wonderful Wizard of Oz, Dorothy thinks she has to go back because they can't afford mourning, among other reasons. "My greatest wish now," she added, "is to get back to Kansas, for Aunt Em will surely think something dreadful has happened to me, and that will make her put on mourning; and unless the crops are better this year than they were last, I am sure Uncle Henry cannot afford it."
In Dorothy and the Wizard in Oz, Dorothy sees, in the magic mirror, Uncle Henry and Auntie Em in mourning, thinking she had been killed in the earthquake.
In Charles Dickens's David Copperfield, after Dora's death, at one point David is asked about his mourning armband and informs the questioner that it was his wife who died.
At a visit to Aunt March's, Amy is shown her jewelry, including "the jet mourning rings and pins." (Jet is black, the only color of jewelry allowed to be worn during mourning.)
When Laurie and Amy meet again in Europe, it is shortly after Beth's death. Laurie notes how poignant Amy looks, partly because of her mourning and "the black ribbon that tied up her hair."
In Andre Norton's Ice Crown, the heroine dreams of the court after the king's death. Another character realizes it was a true vision because she described the (heavily purple) formal mourning, which she has never seen.
In Dorothy L Sayers's Lord Peter Wimsey novel Unnatural Death, a lawyer definitely realizes that a woman who asked him a question — for a friend — had actually asked for herself, when he sees her again, and she tells him that the woman she had asked about, purported a friend's great-aunt, had died, and she herself is wearing mourning.
In the Discworld, it is hinted that female graduates of the Guild of Assassins wear widow's weeds for advertising purposes.
In the Deryni novels by Katherine Kurtz, the widowed Queen Jehana wears all white (suitable to royal widows) for several years after her husband's death. Her quasi-nunlike apparel is also a form of protest against her son's open use of magic and his close relationships with other mages.
In the Circle of Magic universe, Traders (Family-based merchant caravans that travel on land or sea) wear red when loved ones die. Daja eventually adopts a red armband in memory of her family, instead of wearing the all-red clothes all the time. She inspires Sandry to do the same with her black clothes.
In The Serpent's Shadow of the Elemental Masters series, Dr. Maya Witherspoon is introduced as wearing a black outfit in mourning for her parents, who died a few months previous. It is mentioned that she intends to prolong the year of mourning as long as possible as a form of protection, as she is of mixed British and Indian descent and even a brute would hesitate to insult a woman of mixed race that is in mourning. In The Gates of Sleep, Marina Roeswood is, following the death of her parents, outfitted with a new and all-black wardrobe by her Aunt Arachne. Marina wishes at one point that her aunt didn't require her to be in dressed in the strictest possible interpretation of mourning, as normally young unmarried women could wear mauve, lavender, or violet during mourning without offending anyone. She even thinks to herself that she would end up looking like Queen Victoria or a would-be Gothic poetess before her period of mourning is over.
In Once Upon a Time, Regina starts wearing black after the death of her husband and "kept it" as she went public with being "the Evil Queen," saying it suited her.
In The Golden Girls when Dorothy's crossdressing brother dies several heavily veiled, black wearing, women appear at the funeral. They were the guys from his poker night.
Parodied in a Kids in the Hall musical segment, "Terriers." During the instrumental break, Bruce McCulloch comes across two veiled women in black bikinis, dancing beside a grave. He asks them politely to leave because "You're scantily clad and have nothing to do with the narrative; therefore, it's sexist... Wow. That hurt."
"Long Black Veil" originally recorded by Lefty Frizzell. The woman mourning for her deceased lover, who died for a crime he did not commit rather than to expose their affair, wears the long black veil while visiting his grave.
"Ballad of Forty Dollars" by Tom T. Hall. A man watching from a distance, but not actually attending his friend's funeral, hints at a desire to comfort the widow when he sees how attractive she is. He notes:
That must be the widow in the car
And would you take a look at that?
That sure is a pretty dress
You know, some women do look good in black
He's not even in the ground
And they say that his truck is up for sale
They say she took it pretty hard
But you can't tell too much behind the veil
Carrie Underwood sings "Two Black Cadillacs" about the funeral of a man who had left both a wife and a lover. One line in the refrain mentions how "the women in the two black veils didn't bother to cry." Overlaps with Black Widow since it is suggested that the women teamed up to take revenge on him after discovering his two-timing.
The Mars Volta: Referenced in a hypothetical context in "Cassandra Gemini."
The Beatles recorded "Baby's in Black," about a man pining after a woman who "dresses in black" long after her lover's death.
"Whiskey Lullaby" by Brad Paisley and Alison Krauss. In the video, the guilt-ridden ex-fianceé of the deceased is shrouded in a black shawl at the gravesite. Another woman, presumably his mother, is shown wearing a black veiled hat.
Walter de la Mare's Widow's Weeds puns on the trope. A poor old Widow in her weeds/Sowed her garden with wild-flower seeds
In Twelfth Night, Olivia wears a black dress and veil due to the recent loss of her brother.
In The Importance of Being Earnest, Jack wears full mourning dress when he announces the imaginary death of his imaginary brother Ernest. Almost immediately, Algernon turns up pretending to be Ernest, and comments on what ugly clothes Jack has on.
In Street Scene, Rose changes into a black dress after her mother dies. Her father notices.
In The Adding Machine, Mrs. Zero wears a black dress ("I always look good in black," she says) and a heavy veil while visiting her husband on the eve of his execution. He scolds her about the cost ($64.20): "You'll be scrubbin' floors in about a year, if you go blowin' your coin like that."
Barbara Jagger from Alan Wake wears widow's weeds, most likely in honour of her dead boyfriend, Thomas Zane.
Parodied in Something Positive. Attention Whore Kharisma Valetti attends theatre bigwig Avagadro Pompey's funeral in an outfit consisting of a sheer negligée over black cloth bands which barely cover her private parts.
In Rocko's Modern Life, Dr. Hutchison's mother, the Widow Hutchinson is always seen wearing a black dress and veil. Subverted when it's revealed that her husband isn't actually dead.
Victorian tradition gives details for how a widow is expected to dress after her husband's death, and for how long. To cease wearing mourning too soon was a sign of promiscuity.
Jackie Kennedy Onassis at JFK's funeral.
Updated at the Michael Jackson funeral with the women wearing dark glasses instead of a veil. The purpose is the same, to obscure the face and hide teary eyes.