I painted the raised strips on the bed steps of my '65 C10 with Rustoleum undercoating. Since only the raised strips are painted the color of the truck is still there, but you get slip resistance too.

Here's a couple photo's:
http://i645.photobucket.com/albums/...eps%20No%20Slip/DSCF1416_zps8e97deb4.jpg
http://i645.photobucket.com/albums/...eps%20No%20Slip/DSCF1404_zps73bf726a.jpg

Why Rustoleum Undercoating? I painted a portion of my step bumper on my daily driver with the Rustoleum undercoating about 3 years ago. It has held up very well.

In the Stovebolt Gallery ~~ "The Orange Crate" 1965 C10 SWB Step Side Build Thread

Inspired to be different. Different in a way of my own, not in a way that others strive.