I have never fished with a jig on the Cowlitz BUT I've had great success on other rivers. I use different methods for different situations. If the water is high and roily, I use something that casts a dark silluette such as a black or purple. I've also knocked them on a purple/pink pattern or a black/red/white pattern. Sometimes when the fishing is hard, I'll use a piece of cured shrimp (pink or natural) on the end. If the water is "steely green" I tend to use some white and pink in my jigs. When the water is gin clear, I move down a couple of sizes and go with the subtle colors; black, purple, and sometimes green.
I fish under floats that are just above neutrally bouyant so that the lightest stop or hesitation will make the bobber react. You can do this by place lead on the lead in one spot or place split shot down the line (sometimes I use small pieces of hollow core). Keep your line mended upstream from your float so there isn't any drag and get ready!! Hope this helps.

~steelymann~