Seraphiel contains himself mostly to punishing the wicked, but sometimes a good person can still do something evil, and he'll kill them all the same.
"You get that pure, you start seeing the rest of the world as corrupt. The problem is, he was always of a direct turn of mind, so he decided to eliminate the corrupt, rather than, say, converting them or concentrating on providing a good example".
Solaris seeks to exterminate all the "lesser races"... but he changes his mind after discovering that he's only ever dealt with the exiled criminal element of said "lesser races"...
As someone is desperately fighting back against Seraphiel's torture, his mask is knocked off and a hideous demonic face is behind it, suggesting he was evil all along and trying to get people to hate the forces of good.
But then he changes it back, as he's already sent the troops
Gullible lemmings insist that Solaris is good even as he disgenerates them while cackling madly.
Anyone who wears light clothing is seen as evil.
Solaris can think of no better use for his light powers than to shine them in people's eyes when he gets bored.
Seraphiel ignites people in blazes of holy fire for littering and being moody.
Zig Zagged: A photograph of angels of light destroying an orphanage surfaces causing the heroes to turn their back on them. However the angels later revealed those children were demons in disguise. An encounter with more of them reveals that demon children are still innocent and the demonic culture is to blame but at the same time the angels involved were rogue.
There is no correlation between appearance and alignment.
Discussed: "You only ever see somebody using that much Light and Purity imagery when they're either trying to convert people, or, as I assume the case is here, when he's trying to convince himself and others that the wicked, terrible things he does are perfectly justified".
Conversed: "So the guy with the sun motif was the Big Bad after all. I should have seen that one coming".
The association of light with evil results in a world of shadows where food is scarce due to crop die-offs and literacy and electronic media decline from use.