Goldfish are reputed to grow faster & be bigger & more colorful with high light (preferable outside in the sun). Whether that is due to the light or just better water conditions in a pond, I can't say.
I think you just need enough light for the fish to see. Other than that, I don't think it will make too much of a difference. <And some of the fish that normally live in dark (black) water might not be too happy in really bright light also.>
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.