I used hsb because it produces better results. hsb more accuratly reflects how people perceive color. Imagine you used white (rgb 255, 255, 255) and black (rgb 0,0,0) as the two colors. If I used rgb to randomly find colors, basically any color could be used. With hsb, the hue and saturation for black (hsb 0,0,0) and white (hsb 0,0,100) are the same, so the brightness is the only value that gets changed. This will produce a range of gray tones, which is probably what you would want.
Anyway, I find it best to choose your colors in what ever way you like (cmyk or rgb) in illustrator's color picker window and write down the hsb values for my script.
As for the error, I was unfortunately unable to make the script use pattern swatches. In order for the script to work, you will need to delete all the pattern swatches from you document. If anyone knows a way to use pattern swatches as well, that would be great.
Ok, hope that fixes your problem,