This was dubbed, by the creators, as Superman Blue. Gone were the red underpants and cape, the hall marks of Superman. He wore a blue costume with white lightning bolts down all four of his limbs. His chest carried a new stylised 'S' in the same lightning bolt motif. His whole body was covered by the costume, except for his hair and face, which also took on a blue energy hue. Superman Red was exactly the same in appearance, except everything described above was red in colour.
The new costume was in fact a containment suit. In the month leading up to the landmark issue Superman #123, Superman slowly changed into a being made of energy. The suit was made from a fabric which was designed and patented by Lexcorp, and "kindly" donated by Contessa Erica Del Portenza, then the CEO of the corporation. The 'look' of the costume was probably put together by Professor Hamilton (an old friend of Superman's) and Lois, his wife.