Yes, Petrie was right.

The circle square relationship is seen in monumental architecture right through history. The basic idea is that the circle represented the heavens, the square represented man on earth, and his control of the earth. This is an absolutely fundemental concept of the Neolithic Revolution, where architecture moved from circular to square building - it was an ideological shift as well as a functional one.

So uniting these two symbols was seen as creating a place where heaven and earth could meet, obviously important if you want your dead pharaoh to ascend into the heavens. This is seen in early christian churches such as at Hagia Sophia, and in Mosques, and in many modern buildings as well.

As for the Red, there are so many different survey results quoted that its impossible to be certain of anything:

Dave L

43*36' I. E. S. Edwards, The Pyramids of Egypt, Penguin, 1979.
43*22' Mark Lehner The Complete Pyramids. WW Norton and Co Inc, 1997
43*40'. Leslie Grinsell John Bellows. Egyptian Pyramids 1947.
43*36'-11" George Johnson The Red Pyramid of Snefru: Inside and Out, KMT, V8, No3, 1997.
44*44' Dorner, Josef: Neue Messungen an der Roten Pyramide. Stationen, 1998
44*36' W. M. Flinders Petrie, 1887.
45* Stadelmann (1998), Verner (2001) and Arnold (2003) all quote