Is it best to wear warm bright colors & layered outfits (for example a jacket with a collared shirt with a t-shirt underneath as opposed to something simple) for theatrical shots?

If you have an agent, ask them what they would prefer you to wear in your headshots. My son's agent said no layering at all. Bright colors seem to be the norm for commercial shots, and natural colors, like browns, greens, blues for theatrical. If you pick a good headshot photographer they can also suggest clothing to bring.