My wife recently gave me a book I had never seen: Edward Weston: Color Photography. I was not aware that he worked in color at all, but near the end of his career he did work with 8x10 Kodachrome, apparently for a Kodak ad campaign. The prints were made much later on Cibachrome, with printing supervised by Cole Weston. It's a pretty remarkable set of photographs.
I saw a comment by Edward's son Cole Weston that Kodak had given Edward quite a bit of color film near the end of his shooting career, but Edward's health declined before he could make much more than experiments with it. He said that Edward and Brett were the famous B&W photographers, so that left color photography for him.