My work to date has involved a lot of color gradation which includes yarns that are very close in value and hue. Sometimes they are so close it is difficult to tell them apart before they are woven, but the mistake is always visible in the tapestry should I pick up the wrong butterfly.
To keep my colors straight, I use a simple system of tags that I make with masking tape. I should probably buy stock in 3M.
I use a singles yarn and right now am using three of them in a bundle. As you can tell from the above photo, I do ply them on the spinning wheel to get maximal color blending. Each combination of colors gets recorded on a sheet of paper. One sheet of paper for each area of the tapestry where I have to keep track of colors in this way.
Below is the table on which I am organizing the formula sheets and the little balls of plied yarn for each gradation.
If I dye two colors that are close (or not), I can create two more colors in between them by mixing the strands. For example: the following formulas would create a gradation between two colors using three strands of yarn in a weft bundle.
Color A x 3
Color A x 2 + Color B x 1
Color A x 1 + Color B x 2
Color B x 3
As you can imagine, it takes a lot of tape to keep track of all those combinations.
Below are the balls of singles yarn with the dye formulas tagged. From these balls I mix the weft bundles that go in the tapestry.