After supplementing my Giant Danios' flake diet with turtle pellets (reptomin) for a few days, their coloration really developed.
The two younger danios maintained their "normal" coloration, I'm guessing because they're not quite big enough to eat turtle pellets yet. However, the contrast between old coloring and "NEW AND IMPROVED!" coloring is really stark.
Here is a giant danio on flake food:
And now the SAME individual with supplemental turtle pellets
The difference is even more pronounced than the pictures would indicate. The old one was shot using a flash that bloomed the iridescent coloring. The bottom one is NO flash. Cool, right?