I don't wear guernseys to games but I do dress head-to-toe in purple Freo gear. Well head-to-waist anyway - Freo t-shirt, Freo jacket if it's cold, and Freo hat or slouch beanie depending if it's a day or night game. It looks awesome when the stands are just a sea of purple.
No issues with people wearing guernseys if they want. True it's not a good look on those with big guts, but not much does look good on that body shape.
I'm with you estibador - I hate wearing pants to a game ...