I don't remember ever hearing of dimensions turning white. They will get a sickly-looking brownish-yellow if they lose their reference to the model, but not white. There are a couple of things you can check:
1. Is there a Layer of that color, and are these dimensions in it?
2. See if their color has been changed with the Line Color function on the Line Format toolbar.
3. Check to see if the Color Display Model button on the Line Format toolbar has been pushed.