On a serious note, I believe all races existed at the time of Adam (a) and that Adam (a) was a black man. We are spiritual children of Adam (a), meaning we are bound to him and his successors.
According to most of our hadiths (though there are some contradictions about this), Imam Musa Al-Kadhim, Imam Reda, and onwards, were all black skinned color. So last 6 Imams (a) of twelve were black.
I think hatred towards black people is due to Satanic sorcery. It makes people belittle that color when it's beautiful and nothing wrong with it, and also they were oppressed due to Satanic sorcery.
It's Iblis hate towards Adam (a) who was a black man. And Imam Mahdi (a) is most probably black. And there is scripture proof that Jesus (a) was black by the only way he is described in scripture.
As for pictures, people paint all the Imams (a) without black skin so it's same with Jesus (a). Dawood (David) (a) I think was black too according to some hadiths but not too sure about it.