If I have a flesh colored plaque in inner corner of my eye, do I see ophthalmologist or dermatologist? How can they test/treat it?

Eye doctor. Anything that involves the eye itself should be seen by an eye doctor. This is also true if a skin lesion is very near the eyelid.
Ophthalmologist. A yellowish plaque could be pinguecula. You should use artificial tears, sunglasses, and a baseball cap. See your ophthalmologist for further advice.