I'm pretty sure that it's not an STD. I don't know of any STD that causes purplish colored bumps.
Purple/black bumps are not uncommon on the labia. They are sometimes from moles, and sometimes from dilated blood vessels.
However, malignant melanoma can also occur on the labia. Although I think it's not likely, I would recommend that you see your doctor for evaluation. If there is any question, one or more of the bumps can be removed under local anesthesia and examined with a microscope. Best wishes.
My answer is still the same. It's difficult to be very sure when looking at a photo. Your doctor will be able to tell much better seeing you in person.
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