The reason why SR-71s were painted black?

I have found in several books and on-line sources that it was painted black so to radiate more heat – and according to the black body radiation law, that is a sound reason… however, why is it than that most all the other high speed cruising airplanes were painted with the exact opposite – white?

XB-70 white (flew at the same speed as the Blackbird)
Concorde white(when painted in Pepsi blue, speed reduced to M1.7)
Tu-144 white
Avro Arrow white
MiG-25/31 whitish gray/metal finish
Sukhoi T-4 metal-finish/white

Is it maybe that the Blackbird’s black coat was there mostly for RCS purposes? Maybe it was a further development of the “dirty” U-2s Radar absorbent color?