woah, I'd never even considered using tape! I've always done it freehand and left a bit (a few mms) between each colour. Instead of folding the foil, I just put another on top. I'll have to experiment a bit with tape; seems like a neat way to make this faster and easier. Thanks for sharing!
eta. I like doing rainbows in this style.. it's super fun and brings a lot of attention to my chair