How to avoid disastrous paint color choices. And I would know about that.

I once had to repaint a floor 7 times because I couldn't get the colour right. I went through white, straw, green, grey, gold and brown before finally settling on Chili Pepper Red (and only because the paint-counter lady took pity on me and suggested it).  Things would have been way easier with this cool electronic tool, which is now available for free at any ICI paint store.