I don't think the color of the leaves has anything to do with how much light they should receive. The color of the leaves is due to their genetic make up. I group most of my canes together. If one looks stressed then I move it to a shadier spot.

More light usually makes stronger healthier plants which equates to more blooms and brighter colors. Same goes for feeding them. Also the intensity of the light can change the color of the leaves which you may or may not like so experiment. For example, I bought a plant on one of the Keys five years ago. The leaves were almost black but since that time, the leaves are more a bright green with white polka dots.

Here is a pot of some canes I had at the edge of a shade tree so that the front side got direct sun. I had to rotate this pot every week.

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mboston-we have the perfect weather for growing begonias outside. I don't have to baby mine. I stick them under a shade tree (gets some full sun part of the day/year) and give them a spash of water every few days and fertilize. I have the green kind (cane) and some rhizomatous. angel wings and a few rexes and they are all thriving. They are great and colorful and I'm addicted.