It's taken me a while, but I've found an excellent and speedy way to achieve a very pleasing yellow. Here's an example from one of the waiting-to-be-started-painting-jobs:
This sea elf pistolier is a conversion from the Island of Blood set (purchased from eBay). I cut back the original arms and added the spare arms from the outriders/pistoliers sprues after making outriders from that set. For the yellow here I've base coated in Army Painter Matt White, then used the Formula P3 Yellow Ink (pictured) from Privateer Press, with an Orgyn flesh wash in the recesses. This is the first time I've used one of the P3 range and I'm incredibly impressed - the pigment is strong, it's easy to apply and the coverage is smooth. I'll be trying some more of their range over the coming months, along with some of the other Army Painter primers, when I get started on my long-desired Vampire Counts army.