For "color first" to make any sense to me as a design process, "first" has to mean primacy of place, not of chronology.
My experience is that all at once, in a flash in the shower or while driving home from work, you fit together four things: an insight into some kind of source material, an insight into roleplaying as a practice, an insight into real people and real human nature, and a batch of seed content. None of them comes first chronologically in the design process, and none of them can trump the others in importance. I mean, you might be musing about one or another of them first, but the design process can't start until you have all four, and from that point on they're coequal.
Color isn't a fifth thing, a concern to balance against those four, it's a quality of those four things. Apocalypse World's MC agenda, principles and moves are system color (and express my insight into roleplaying as a practice). The post-apocalyptic stuff in the game design isn't it's own thing, it's the color of the game's seed content.
Now, what DOES happen is that some people strip color out of their insights and their seed content, and design from a more abstract position, where other people (like me) enthusiastically embrace all that color. Dogs in the Vineyard isn't an abstract detective procedural game, which it could have been I suppose, like Shock: is an abstract social SF game.
So yeah, color first design in the sense that the color of your insights and seed content is of first concern, not that color came somehow first in the design timeline. Who even KNOWS what came first when inspiration struck.