return an integer representation of this color. Utilizes bit-shifts to store the color as one 32-bit integer, like so:
0bAAAAAAAARRRRRRRRGGGGGGGGBBBBBBBB aka 0xAARRGGBB
0bAAAAAAAARRRRRRRRGGGGGGGGBBBBBBBB
0xAARRGGBB