why is it bad to where red at a funeral?

Answer 1

as wearing black is considered to be a sign of respect so actually wearing another colour is just rude [according to certain rules]

certain other cultures consider white to be the colour of mourning so it really does depend on where you are from.

As for me I would not dream of going to a funeral in anything BUT black

Answer 2

You are supposed to be mourning so you are "supposed" to wear dark colors.