I Don't Have Any Skin Issues Iam Blessed With That.

I don't have any skin issues iam blessed with that. But some times..... when am hurt deeply by some bodies words/behavior (or) feeling very bad from inside (or) if I cry badly my skin color changes and become darker specially on my face because I didn't observe any other areas but my face completely changes color to darker and it can be seen clearly don't have to observe particularly. Can I know the reason behind that and any medication??