In order to make any kind of informed decision as to the color of the dye you’ll need to mix for any black and white print, you first need to know what the dyes you are starting with actually look like. You can’t tell when they are wet, so make a sheet with a smear of each color you have, label it, and let it dry. You’ll use this sheet all the time so keep it safe in a folder with other important spotting notes and samples. You may want to make another sheet with smears of some of the more popular mixes you tend to use.
This is my basic color sheet. I can create just about any shade I may need in order to match a print starting from these standard dye colors. These are all Marshall’s basic colors except for “B,” which is a mix that I use all the time.