If you are using Maya 2015 or newer, you may notice an issue where parts of the rig show as black or shadowed instead of their normal color. This tends to occur mostly on older rigs.
This problem is caused by an update in Maya 2015 which turns off "two sided lighting" in the viewport by default whenever a new scene is opened. You can fix the problem by going to the viewport in Maya, clicking on "Lighting" and making sure that "Two Sided Lighting" is selected. This will need to be repeated in each viewport you are using.