I have done best with fushia colored flies, especially a fushia bunny leech tied with some hot pink Krystal Flash tied in at the head that is nearly as long as the fly. Hot pink has been another color that has worked for me as has hot orange combined with either hot pink or fushia.
Also, I've found that rather small flies (at least by most people's standards for chinook) of #6 worked best for me in low, clear water. I found a nearly dead drift presentation to be best. And in low, clear water, I do so with a floating line and long leader (13'-16') that has a 12#-13# tippet.