Here's my best attempt at answering your questions:

Color - Depends on water conditions. For example: big, bright, and gaudy in high, off-color water, small, subtle and darker in low clear water. (not always though, nothing is absolute when steelhead fishing.) My best advice: What colors do YOU have the most confidence using? Use those colors.

Whitefish - Drift a small whitefish fly tipped with a maggot in the current seams.