Second, this is the way I do it. Paint them in fairly unremarkable colours so they are present but they don't interfere with the model. The colours I use are dark browns and greens to make it look like perverted local plant life that is part Tyranid. This colour scheme is easy to enhance on larger pieces on the bases of more important models, such as my Trygon and Malanthrope.
That's exactly how i did it on the first batch of stealers i painted up.

Do you have a picture of those in the boards gallery?
I'd really like to have a look on those.
I'll see what i can do about getting a photo or two up. I've been meaning to take some for a while, a friend wants to see what this crazy "dipping" technique i told him about looks like.