The actual code will vary, depending upon how you're using the background image. If you're entering an image under Projector > Site > Design > Cover page and telling it to center it and repeat it (like a texture image), then producing the same thing on the About page would require this in Projector > Advanced > Custom code > CSS:
background: url(graystone.jpg) center center repeat;
Use the same file name, of course.
But if you're giving it an image and telling Projector to stretch it to fit, the code would be:
background: url(myimage.jpg) center center/cover;
The skin should probably be updated to do this automatically, though I could argue against it, since the About page shows text over that background image.