Define "decency". I've lived through 2 fashion periods where women's nipples were visible thru their blouses or dresses and even today many women choose tops so that their nipples protrude. Same thing for guys and tight pants, some men chose them so that the outline of their penis is readily visible.
Either you are very young, extremely oblivious, or both as far as current events go. Women not wearing a burqa have been arrested and even stoned top death. Similarly in New York City, the laws covering nudity (last I heard) make no distinction between men and women. Anywhere where it is legal for men to be shirtless, it is legal for women as well.
And anyone with even a poor education knows that some hunter/gather cultures tolerate complete nudity (especially in children). So, it is ridiculous to ask about cultural absolutes as far as nudity.
My guess is that a culture should tolerate only exposure of skin which is sanitary - that is doesn't significantly spread "germs". Both sweat and waste from the anus, urethra, and vagina (as well as (lactating) breast leakage) would be expected from nearly all healthy individuals. Fluids from unhealthy or injured individuals also needs to be considered. Given our (current) anatomy, it seems to me that in an environment where temperatures (winds, humidity, sand, pollution, UV,...) don't require protection, then a loincloth would be a minimum.
However it seems to me that there's almost no advantage to having photosynthetic skin in the groin, armpits, inner thighs or soles. To be effective, the photosynthetic skin will be more vulnerable than skin might be without it. Although I can think of several tropical plants with very tough leaves, in general the surfaces of leaves are not very robust. So, like everything else, any redesign of human skin and metabolism will have both advantages and disadvantages.
One (obvious) function of modern clothing is moisture control. Seems to me that we might be able to have moisture permeable, colored clothing which only slightly filters light in the blue to orange part of the spectrum (violet and red colors would take out the least energy). Thickness would matter: thicker, greener clothing would be a status symbol, as would multiple layers.
Hair would be counterproductive, but sunglasses (or modified eyes) would be useful. I should mention that obviously someone living at the North Pole would have different optimal trade-offs than someone living at the Equator, similarly someone living in a city or rainforest compare to living in the desert.