Hollywood reflecting the fashion of its day or inspiring the fashion of its day is rather like a chicken/egg scenario. It’s sometimes difficult to know what came first.
In some cases, Hollywood ruled the day, as in the famous “It Happened One Night” (1932) example where Clark Gable removed his shirt when undressing for bed and ta-daa! Gasp! He wasn’t wearing an undershirt! Manufacturers and retailers of men’s underwear shuddered as sales dropped for undershirts.
We can also point to Sonja Henie and her fabulous white skates. White boots for girls’ figure skates is so standard now that we may forget that when ice skates made that first amazing transformation from just the kind you clamp onto your shoe to the kind that has its own built-in boot, they were all brown or black no matter if the skate was for a male or a female. Sonja Henie’s white skates, her trademark, changed the industry and fashion for skates.
Women’s pants were made acceptable by the Hollywood stars which adopted them in private life, even if they were not seen in many films.
Reportedly, colored shirts for men in public was the result of John Gilbert’s attending a party without changing the shirt he wore for shooting at the studio that day, which was blue. Photographers and graphic artists out there will know that light blue photographs lighter and softer than white in black and white photography. A white shirt will cause more glare from the lights, but a soft blue absorbs the glare and photographs as white. Apparently if John Gilbert can wear a colored shirt to a party, it must be the thing to do.