All three infected characters with purple eyes are shown to be weak or disabled in some shape or form. Grandmother is an elder, Mousy is strongly implied to have no legs, and a note in the Safe Place indicates Mimi is colourblind and has low vision.
A lot of the red-eyed infected wield incredibly dangerous weapons, like axes, flasks of acid, large swords, fencing posts, planks with nails, anchors, guns, mallets, tridents or wooden stakes, and other infected with red eyes also show other signs of danger (Willow, Pandy and Kitty are all members of The Silver Paw, Penny gets possessed by The Insolence in Book 2, Zizzy fought off an entire horde of infected soldiers alongside Pony during Chapters 11 and 12 of Book 1, Kraxicorde is a giant kraken, Daisy is part of the military).
