dark spots on foot

I have a question concerning a few spots on my foot that are darker in nature than other parts.
I am curious as to whether or not this could be plantar warts or not.
I feel them and there is no texture to it, it just feels like normal skin.
It also does not feel like there is anything beneath the spots, no hardness, no bumps, etc.?
Is there any way that I can be sure.
I have scheduled an appointment, but I cannot see the doctor until August.
These spots are very similar to the dark spots you sometimes see in the palm of your hand.
COuld this just be my skin?