I call this fly the"Bruiser." Yes, it is a big, meaty chunk for hungry fish, but it is black and blue, too. This WB is definitely a variation of the egg-sucking leech, which usually is tied as a black WB with an orange or red head. I once read that rainbow trout are attracted to the color blue in flies. So this seemed like a natural color combo for those early season rainbows that cough-up hatchery pellets when you land them.
Note: you might not (probably won't!) find in a fly shop all the different colored beads I use. Last winter my buddy Jerry Bernier bought a big supply of various colored glass beads and I bought a couple bucks worth off him. The red, pink, yellow and clear ones make great egg-flies. The others show up on my woolly buggers and larger soft hackle flies.