He is not treating you rightly that is What I gathered from your mail. Reasons may be best known to him and not only your dark skin. First, ask question to yourself that why his behavior changed. If you find any reason in your attitude which might have caused this then try to rectify it. If you introspect and convinced that nothing from your side then tell him that his behavior is hurting you and you want to understand the reasons. Assure him of changing yourself if reason is pertaining to you. Insist on honest and clear discussion on the issue, if he tries to evade the discussion.
If nothing works out then you should be thinking of separation and not asking him to give divorce. Why you should ask him to give divorce, you should have courage to take decision and should not ask him to take that, which he is not going to do so long he is comfortable with the issue.