I'm mulling over posting something on color myself, but it's so entangled with other subjects that I might just wait. I'd at least agree here that HSB/HSL is the way to go for getting colors chosen. After that, use your knowledge of color to tweak the proper atmospherics and reasonable leaps of 'Hue+saturation' and Luminosity between colors. I have yet to really use rgb for choosing colors, but it's certainly a valuable resource.. much "asian" style work seems to gravitate more around RGB...
I think it's good to point out Helm's artistic development.. his colors are, in my mind, more grimy/mature (bitmap brothers and demoscene inspired), as opposed to the stuff seen in games like phantom brave (where dithering is very uncommon, probably as a preference in workflow) where works appear very pristine; 'watercolory' work (also rgb oriented)... Which is really a matter of taste. Color palettes which have multiple ramps to bridge between two or more colors are more suited to dithering (more like demoscene), whereas..... what I'd call the 'korean' style of color work, interestingly enough, seems to be more fixed-palette based than anything else (basically 'tested' colors that one need not focus on so work can be done faster), and they seem to lean towards RGB color selection.
When I find the time, I'll do a proper paper on this with examples.