It's just RGB... it's hardly a secret. As for picking values, just use the GIMP's color picker and you'll get it easier than doing it manually. (You have to recheck for the right shade... it's much easier to use a external util.)
Oh, and when using parted... don't try to ignore the warning to umount the partitions, especially if it's the / partition... (I've gotten away with the others...
)