The color of the dim or inactive button text (like "Back") is controlled by a text object behind the back button. There is actually a text label behind the field zz.BackMagic.cr which just says "Back" (and another one saying "FWD"). You can simply change the color of these using the text color tool in layout mode.
The active or "lit" state of the button is controlled by the text color applied to the field zz.BackMagic.cr itself. Again, you can simply change this with the text color tool in layout mode.
Note that since we're using layout tools to control these colors, you can have these buttons look differently on different layouts if you need to.