Unify custom power colors

[blehz-be]

Power color for text was not the same as for bars. Also the pastel calculation was not uniform.

[shagu]

Thanks, but I did that already a month ago and had to revert it again.
There were too many people complained about having bad/unreadable colors now.
By that the text on power bars became barely readable because of having the same color.

Here's the revert: 28762f8

I think what it really needs is an option to define custom text colors aswell.
But I didn't had time to review this yet: #1577