Guess what, there isn't one and there won't be for a while.
Hope this helps somebody out there.
It may be useful to use what web developers are pretty used to for colours. Parsing to rid of the # character for parsing not included.
This function takes a value like 0xffffff then returns an SDL_Color type. This is designed for use with SDL and OpenGL, so if you call SDL_GL_SwapBuffers() in your graphics loop function, then this function is likely for you. In SDL, OpenGL space is represented in BGR rather than RGB.