No sir. You were actually correct and I capitulate.
I took a look at the numbers again and there are more blacks incarcerated than whites. I could have sworn it was the other way around but it isn't. It's by a slim margin (40% black to 39% white) but the numbers do not lie so I admit that I was completely wrong.
For the 2nd question (white or arab) it's still white though.
Please note:
The rates of incarceration for black has been steadily dropping over the last several years whereas rates for whites are slowly climbing. Another few years and the answer to the first question may very well be white. I'll take that bet in 3-5 years then...