Do you smell that? Its the smell of actual painting advice. Mmmmmmm.... breath it in, its AP certified non-toxic.
Moving along. I covered the qualities of various paint types and brands in pretty good detail a while ago (see the On Paint series). Now its time to do something similar for another category of paints - colors. Not all pigments are created equal and there's a world of difference between how one approaches painting dark grays and bright reds.
The 'Eavy Metal team may make painting look easy, but there are a fairly large number of colors that cause difficulties for painters who are just starting out (often times vets can get caught up with them as well). For whatever reasons, these colors have some characteristic that makes things more difficult to work with. Unfortunately, there very common colors that people want to paint.
Over the last few years, I've learned a thing or two about how paint these problem colors AND make them look good. Time to share my knowledge in a new series with an overlong title. Underlying all of these suggestions is my continuing insistence that thin coats of paint are best. Obviously, its not worth the time to do this in every situation, but please keep it in mind.
I'll include pictures when I can (all of which are the copyright of the owners unless otherwise stated).
First up is a color that is fairly situationally difficult.
For clarity, I'm talking about pure, bright yellows. Lemon yellow and so on. I'm talking less about ocher/ochre type colors and other such yellow browns. Even pastel yellows (ones with some amount of white in them) are much easier to paint. Its primarily just those really striking yellows that grab everyone's attention. Like our Imperial Fist friend over there.
Yellow pigment has lousy coverage. Especially when it has to go over dark colors. Its thin and its often streaky. This is a problem for people who like to prime their models with black. This is also a problem for mistakes that get painted on to yellow. It can be very difficult to fix an errant streak of paint on your yellow areas.
Lucky for you, there are few tricks to making yellows work for you AND to make them pretty easy. First, if the majority of your model is going to be yellow, its probably a really good idea to prime with white. And by 'probably a really good idea', I mean 'prime your damn models white if you want yellow as a major color'.
A white primer will do wonders for alleviating your coverage problems. This goes for painting yellow details as well. Another alternative solution to 100 thin coats of yellow paint over a dark color is to hit the area in question with a quick layer or two of white. As white has it's own coverage issues, I often find that an ivory color works much better. Go figure. More on this at a later date.
Speaking of layering, most yellow goes lousy over black, but much better over other darker yellow/yellowish shades. However, this will affect the final color of your yellow as yellow is so prone to translucence. Lemon Yellow wont look too good over an ochre or light brown.
So this option works best for dirty yellows like P3's Sulfuric Yellow. I'd also like to point out the Citadel Foundation color, Iyanden Darksun, as a readily available example of what I mean by a yellow ochre. It's the color that the above Lamentor is almost assuredly painted in. Iyanden Darksun also has pretty good coverage too.
Its at about this point, when the yellow starts being pushed towards brown, that the yellow paint gets markedly better coverage. The further towards brown, the better the coverage. Making brown/ochre yellows a viable option over a black base coat.
Though not as strong a pigment, yellows on the pastel side (like VMC Ice Yellow) also have better coverage than regular bright yellow. However, the coverage can still be spotty depending on the exact color and paint formulation. Again, a white base coat is the best option for bright yellows.
Yellow isn't actually all that hard of a color to deal with as long as you're aware of its shortfalls and aren't married to black primer. Layering can be your friend here as well. As to what to do about mistakes on yellow, try to be careful. If the worst happens, remember that layering and thin layers are your friend.
Finaly, make sure you pay attention to the color differences between various yellows to make sure the shades your using are complementary.
[Edit]: Personal anecdote: the futility of trying to airbrush yellow over black is especially severe. I might as well have been pissing on the model for all the coverage I was getting out of my Vallejo Model Air yellow over black primer.