I agree with Dave's comments re: when the slow down took place and with Eric's on possibly upgrading cards/drivers to clear up graphics problems. Here's where you check on any new hardware requirements:
When Wildfire first came out, this was observed a lot and PTC published a TAN on it. I'm sure it's still around if you can figure out how to find it. It's probably three years old by now.
Anyway, the default shaded color and its properties are not modifiable. If you go into 'View>Color and Appearance', the first ref_color (upper left corner of Appearance Editor) has all the controls greyed out for changing the color on all the tabbed pages, Basic, Map and Advanced. You could just create your start part with some basic geometry and set it to a user defined color. But graphics settings on your computer, unless they're tailored to Pro/e and OpenGL, probably won't have much effect.