Okay, so confession time: I really only bought the Classics Ultra Magnus Vs. Skywarp set so I could get my boy Skywarp. I've never been a fan of the whole
"White Optimus Prime Is Ultra Magnus" school of thought. The Magnus repaint has grown on me, however, and I decided a few little paint modifications would endear him to me further.
If you noticed, the Magnus on the box is painted quite differently from the one you get inside the package.

I wanted something similar to that, but as I'm even less of a fan of the baby blue as I am of the
WOPIUM movement, I decided to spruce him up with three small modifications:
1) Paint the white Forehead vent and silver Face mask
blue.2) Paint the blue Eyes
red.3) Paint his blue Light Pipe Head
white. The first thing I did was remove the screw in the back of his head and pull out the Light Pipe part of his head, since the eyes are part of this piece and it's easier to paint them that way.
I painted his blue eyes classic Magnus red, let it dry, then screwed that part back in. This much is so easy that with a paint pen you could have it finished within seconds.
Then I mixed up a small batch of blue Pactra acrylic enamel that approximated the same color as the paint apps on his arms and crotch. Using a Games Workshop detail brush, I filled in his forehead vent and gave his silver face mask a good once-over.
The last step was highlighting his muttonchop cannons with a dash of silver, just for the hell of it.

So there you have it. the whole process took maybe a half hour, and the results are significantly better, IMHO.

I am still in the process of painting the back of his head white, to conceal the light piping, but it's taking multiple layers of paint and a considerable longer amount of time to accomplish. Light piping is a neat idea in theory, but in actual practice I think it detracts from the appearance of the figure when a chunk of the head is a completely different color. I prefer to do away with the 'feature' whenever possible.