I just used the 70-7551 to install a Pioneer AVH-P2400BT in my wife's MO this weekend.
You are partially correct, for the most part, the colors on the 70-7551 harness match the colors that Pioneer is using on their harness.
You shouldn't just trust the colors though, look in your radio manual for a diagram showing the function of each color wire. There is a color code guide on the back of the package of the 70-7551 as well, make sure that the wire functions(not just the colors)of the two harnesses match. You might have wires in the Pioneer harness that are not use. I had a couple wires that weren't used.
The RCA cables on the 70-7551 connect to the Pre AMP outputs on the Headunit: Grey is Right Front, White is Left Front, Violet is Right Rear, Green is Left Rear.