I've been dyeing a lot of fiber lately. (Hint, there'll be some new things coming to my Etsy shop shortly.)
I love playing with the colors...I think that's one of the reasons I enjoy watercolors so much. There are a lot of similarities between acid dyes for wool and watercolors. They are both transparent, so you can layer and glaze the colors. You can decide how saturated you want the color based on how much water you add, you can mix colors to create a custom blend and so on.
Anyway, I've been having a lot of fun with it!