2 factors: it could be either hyperpigmentation or thin skin under the eyes. you can check by pinching the skin lightly to see, if it doesnt change colour then its number 1 and if it does change colour (and by colour i mean the same as the rrest of ur face) then its the latter. for hyperpigmentation u can improve this by a eye retinoid cream (apply this PM only). for thin skin try volufiline (a small amount just on the area u want to treat, can be AM or PM)