I noticed a problem with Material Dark skin.
It can best be illustrated in this picture:
[attachment=8755:Wrong Color.jpg]
As you can see, the text color in the TsSpeedButton is wrong if the skin is set to TB_BTN. The strange thing is that it is OK in a TsTabSheet with skin set to TB_BTN
Here is a test project. It appears that TsButton has the same problem. If you click Cappuccino, you'll see that dark skins can work correctly: [attachment=8756:MatDark.zip]