The standard colour is Color.WHITE
. The actual colour of the image/texture is actually multiplied by the colour you set on the button. Color.CLEAR
is a colour with an alpha value of 0 which means 100% transparent = invisible.
Color.WHITE
means that each colour component of the original picture is multiplied by 1 and thus will not change.
skillButton.setColor(Color.WHITE);
will "reset" the button to its normal colors.