Quote - Is this effect not to do with gravity and blood flow, to an extent, to?

Well, it might be. But since there exist a great many character sets out there that do not exhibit this problem at all, I'd think it's unlikely to be a problem common to most people or even most photographers.

I guess some merchant resource sets get used a lot, and it just happens to be that one or two of the more popular ones have red legs.

Some of the characters I've bought have such outstandingly red legs, I actually thought they were accidentally from a different set, until I noticed it happening in several of my purchases. It's a shame, too, because the top half of those sets is usually very nice. But the legs just totally ruin them for all but portraits shots or pants suits/jeans or very long dresses. To be sure, I make a lot of renders of people with covered legs, so it's not the end of the world. But if I can avoid buying red legged people, I will.

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PoserPro 2014, PS CS5.5 Ext, Nikon D300. Win 8, i7-4770 @ 3.4 GHz, AMD Radeon 8570, 12 GB RAM.