为什么我不能将colorkey用于SDL纹理？

I wrote up this simple C program to test basic SDL 1.3 functionality. Everything works, with one minor problem. The colorkey doesn't get converted. I'm loading an 8-bit PNG sprite file where palette index #0 is the background color. I'd expect to see only the sprites displayed, but what I get is the entire image, including the background color.I wrote up this simple C program to test basic