When you click on changeskincolors in Skinstudio a new window will open, up at the top it says in a box with an arrow "Show me the skincolor presets"
Click on this and another option will drop down Imediately, it says "Show me the skindefinedsystemcolors" -click on that and find "WindowsText" Click on the "WindowText" Color and Change it as desired using the change color-button to the right inside that window...