Seems like you figured out your yellow issue but I figured i'd throw this out just in case.
I've had a lot of success with my yellow technique the past. Check out some of the stuff in my gallery to see if this works for what you are aiming for. Here's how i'd do it.
Base black - lightly drybrush grey to accentuate the edges
Paint yellow areas with an eggshell white (elf flesh I think) as this will be much easier to apply in fewer layers than a stark white - Highlight those areas with skull white. it's important to get a nice blend for shading. Shade your low lights with a mix of Skrag brown / elf shesh. An easy way to get your blend down would be to drybrush those areas with more pressure rather than wet blending if you aren't use to it.
For the yellow - I either use a yellow acrylic ink or vallejo yellow ochre. You can apply these very thinly, usually in one layer. The idea is to tint the colors you've already put in place so they show the shading below.
For the eyes I think a red orange would look pretty solid
Hope this helps! I'm really digging the color scheme you're doing for these guys