What kind of make-up would I wear for a "natural look" for a friends wedding?

I'm a bridesmaid in my friends wedding on Sunday. Our dress is purple(lapis to be exact) and our sash is clover green. She wants us to have a natural look, but I'm not very good at putting on make-up and the only make-up I wear is black eye-liner and black mascara. She wants our make-up to be very "daytime" and her wedding is outside. Any tips on what I should buy? I dont want to spend a lot of money buying stuff.