However one might want to justify or rationalize the TMP uniforms, I do not feel that they succeeded as great wardrobe for Trek. The latter film uniforms did,and are now as iconic as the TOS uniforms. It's important for filmmakers to know what works cinematically, and the brick red jackets did.
I laugh at anyone who tries to pass off the pale color pallette of TMP as poor video transfer, they were pale pastel colors on film too, I've seen MANY film prints, I WORKED with the film prints. They were supposed to be pale, softer and more subtle than the vibrant primary TOS uniforms, it just so happend that choice was a poor one, IMO. And yes, they do look like pajamas. The truth hurts.