The color picker opens at flat black, regardless of the color setting of the subshader. So when you click on it, it resets the highlight subshader to something like zero.
I don't mind tweeking the settings, but find with my system that I only get accurate settings when I have my anti-alias set to (at least) "good". Anti-alias "none" or "fair" gives a shader that is very different than the final render on "good" or "best". I assume that it is a result of my screen and graphics card, but haven't compared with another system.
An hour spent tweeking the settings while on "fair" anti-alias is a total waste of time. I have relearned this lesson several times. {insert pout here}