select the text, and then change the color. If you want to permanently change the color, you probably have to modify the typeDef. I would suggest not changing the LV typeDef, because it will change all instances of digital indicators. Instead change the typeDef and save it under a new name.
To change that, drop a digital indicator in the front panel, select it and then Edit>>Customize control. A window will open where you can change the indicator and save it under a new name (*.ctl). Start using the new control from the file now.
Hope this helps
A Rafiq
National Instruments