Pyramidhe@d, gaunts are not viewable in the army painter... however, if you want to know, the new army painter is a bit different from the DoW1 one. First of all, you can't make your custom colors, you have to choose between A LOT of standard ones, which are the reproduction of the normal Citadel Colors; you can also choose a pair of metallic colors! That will also stop the "neon armies" that I used to see in DoW1. xD
Then, only in the Space Marines army builder, you can choose the color patterns: for example, you may use one where you have different colors for the body and the shoulders or you may use another where you have the entire body with different colored halfs. There are 4 patterns in total and, I repeat, they are SM only.
BTW, isn't there already a Gaunt in THW? Anyway, I can take a Gaunt screenshots if you like. ^^