Define I knowed he was white inside…

I know, this sounds pretty bad. We must examine the context of the book. Huck is an uneducated product of the old south. Saying that Jim is "white on the inside", was a complement. The notion that white people were inherently good, trustworthy.....was ingrained in white culture. Similarly the notion that black people were the opposite was just as ingrained in white culture. Huck's relationship with Jim did not penetrate the greater black/white colour barrier. Thus Jim, being white on the inside (even though he was black) meant that he was a good guy. This was Twain making a progressive statement, believe it or not, for the time.