Your son is six. He did not make a racist comment. He made an honest comment that showed he is aware of what racism is, and is, therefore, aware that he escapes it via skin color. Given his observations and awareness, he shared an obvious judgment.

I'm glad I'm not disabled. (Or differently abled.) It doesn't mean that I'm selfish, egocentric, judgmental, or the like. It means that I recognize that some people, through circumstances not of their choosing, have fewer choices, are viewed differently, are treated differently, etc. I'm not going to try to give you parenting advice, but I would say first, what you said second, which is that it's our job to make sure that everyone gets treated well no matter who they are.

Children certainly notice differences. We don't all look the same! But the meaning we attribute to those differences are what children notice and, soon, incorporate into their attitudes and behaviors. Your son is definitely not racist. Depending on your choice of rewards, he deserves recognition that he's honest, thinking, and sensitive.