Is it normal for the underneath of my top eyelid to be a white color?

There is a structure in both the upper and lower eyelids called the tarsus. This is a condensation of collagenous tissue that appears a bit whiter than the conjunctivae. If you have this paleness under both upper eyelids chances are you are looking at your tarsus. If however, there is a significant difference between the two eyelids, you should have your eyes evaluated by an ophthalmologist. There are conditions of the eyelid that can cause a leukoplakia or whiteness to the tarsal conjunctiva (undersurface) of the eyelid. These should be diagnosed and treated as appropriate.