I do think those parts of you which are not exposed to the sun would give you a better idea of what color you “really are”, like for example, I am constantly exposed to the sun so I have somewhat tan skin, but my legs, torso and underside of my arms which are usually spared the rays of the sun are pale. The parts that don´t count are the palms of the hands and the soles of the feet because they’re naturally lighter than the rest of the body (even in dark skinned people).
Here’s the thing, tho; during winter months, or when I spend a lot of time indoors because of one reason or another, the skin in my face and arms DOES revert back to its lighter tone.
I also know someone who had naturally dark skin but then because of some melanin-related problem started becoming REALLY dark, yet after some treatment (not sure what exactly) she reverted to normal. So I would say this sort of thing is not irreversible.