The bride sounds like the controlling type. You are under no obligation to attend either the shower or the wedding. Gifts are optional, though it's nice to give one when you can afford it, and attendance at a shower implies you plan to give a gift. The word is 'implies', though, not 'requires'.
If you feel you must give a gift, make a simple table topper in the colors she told you she prefers that YOU wear to her wedding.
Tell her that it is priceless, one of a kind. I'd hold off on telling her that if she doesn't like it, you'll take it back.
And don't wear the colors she wants you to wear. You have to have some fun...