The way I'd attack that problem is create a bunch of NSBezierPath's that tile the surface you want to cover (and a little over, so we allow clipping), then fill each of the paths in ur tiling with the NSColor you made. Does that at least give you an idea of what to do? I'm kind of tired, so no coding for me now. Just post again if you want some explicit code.
HTH,
F-bacher