Rather than mix my chosen color and then dye the wool, I decided to dye the wool in the individual base colors I use, then blend them together in the proportions called for in that color formula. Say I started with 100g of fiber - if my "recipe" was 68% color A, 20% color B, and 12% color C, I'd use 68g of wool dyed in A, 20g in B and 12 in C, and blend the individual colors. This process takes advantage of optical blending, in much the same way pointillism does. It creates the appearance of a solid color, but with greater depth and interest, especially when seen from up close.
Here's what I did. I weighed out the fiber for individual colors into gallon zipper freezer bags (labelled, so I would know what color went in which bag), added a solution of water and Synthropol (a surfactant to ensure the fiber wets out evenly), and let the wool sit for a couple of hours. Then one bag at a time, I carefully removed the wool and added the appropriate amount of dye & other chemical assists, then returned the wool to the bag. I found it important to remove the wool before adding the dye, otherwise most of the color would end up in one spot on the wool, rather than evenly dispersed.
It spins up into a wonderfully lofty DK/Worsted weight 2ply! I'm very pleased with the results! One of the things I like about this process is that it allows me to turn what would normally be a flaw into a "design element." This particular fleece is fairly fine, and despite my best handling is prone to neps. These little clumps of fiber are generally considered undesirable in an undyed or solid colored yarn, but when the colors are dyed before being blended, the neps make nice little flecks of color in the finished yarn that I find I rather like!