Nail polish is fine and has multiple colors just paint the end you hold and it doesnt have to cover the entire handle a dot or square would do. If you are worried about ruining them many hardware stores and key places sell a set of color coded rubber or silicone rings that slide over the outside of the handle.

You can use nail polish on the end where you hold it when you insert the key. After that you can get a toothpick and some white paint and write which key it is on the painted color ( house, car, work, etc.) Remember that you paint the part that you hold, not the inserting part!

I like to use nail polish to color code my keys.

I've started accumulating more keys on my key chain since I'm becoming more independent. It's not that I can't tell the keys apart, I just think it would be fun to decorate them. I want to paint them with nail polish, but I'm worried about ruining them. Would they fit wrong if I painted them? Or should I use markers or something? I'm screwed if I ruin them because my family's gone until Wednsday and I need to be able to get into my house and my neighbor's. Also if you have any suggestions I would really appreciate it, thanks!