Underpainting? (not to be confused with undercoating)

[vikotnik]

Perhaps You should try the transparents by Vallejo first. They have some very nice transparent paints that have the same consistency as the other, opaque, paints.

[Rhoderic]

Maybe later. I'd have to order the paints first, and everything.

Although, I do notice Liquitex makes a gel medium (for acrylics) that's described as "extra thick" and apparently makes paints more transparent. I might go pick up some of this at the local artist's store tomorrow.