I have never blocked anyone because of what or who they are - I have only blocked people I felt were offensive to me - In recent times I felt I was too sensitive about it so I have since unblocked everyone - Currently I am blocking no one.
I block because of personality, and usually I only block perverts. One guy sent me a link and I asked what it was. He said rate me so I was like um ok. Well, it wasn't a face. IT WAS A DICK. So I cursed the guy out and blocked that little bitch. If i don't like someone I either stalk them and down vote them :^) hehe, or I ignore them. So it never has to do with race, religion, custom, etc.
If someone blocks you due to you race then consider them to be doing you a favor. :) What does that honestly say about the low value of their intellect? The poor quality of their thoughts? The filth and grime built up in their mind? Do you really want someone like that to be apart of your online environment or any environment of yours at all?
Are you sure you were blocked specifically because of your race? Did they openly explain that to you?