Get some graphics in CHR format and try this program:
http://nesdev.parodius.com/nsa01b.zip
(it also loads a 16-byte .pal file for the palette, if it's available)

The left mouse button will set the attribute, you can kinda how it works for the background.

The 4 colors you mentioned would be fine to use for one set, as long as one of those colors (black, I'm assuming) is the background color and stays consistent through the other sets.