Transparency of the skills window is too high.
I like a little transparency, which makes all interfaces easily readable but also shows what’s happening behind it. My UI transparency is setting at 31/100, (of which 100 would be maximum transparency).
As the skills window is huge and only a temporary element on my interface, it’s going to be in front of other UI elements when I open it. But if there is a little transparency (not a lot, the slider can go much further to the right!) this means the skills window becomes pretty chaotic and unreadable, as shown in the picture below.
(Transparency too high, clearly)
My suggestion: significantly reduce the default transparency of the skills window. Or remove the transparency.