JM,
Not so sure about that. Audrey Hepburn was not only a cinematographer's dream, but carried around a genius level I.Q. between her ears to go with stunning looks and the grace of a trained ballerina. Kate Hepburn (who I think is actually the most attractive woman who ever lived) did not so much walk as march - always with a sense of purpose. Audrey seamlessly glided through her blocking so smoothly, it looked choreographed on air.
Greta Garbo was retired by 1941 - so you've got to factor that film in America was still in its adolescent stage. To the best of my knowledge, the only color photos of Garbo were production stills; all of her films were in B&W, which are gorgeous, but largely an apples and oranges comparison.
It does seem odd to me that (as far as I know) Garbo never appeared in a "three strip" Technicolor picture (Wizard of Oz).