In my observations the environment contributes a lot of colour to surfaces via bleed & ambient & bounce light. IMO it's a mistake to try to eradicate it.

Take skin, for example. It takes on a different appearance on a cloudy day than in bright sunlight with a blue sky, and whether a person is stood in the shade of a tree or next to a red-brick building. So much of these variances in appearance are due to reflected light of one sort or another.

It is difficult to be scientific about the degree to which sources such as HDRi's and the systems we're using to simulate light in 3d are delivering this light (and colour) though. We sometimes look at a render and think it looks all wrong, but we're making assumptions based on the relationships and balances between surfaces that might not be at all well simulated. Sometimes it is because the systems are indeed out of whack, as bb has shown us with the relationship between diffuse and IDL in Poser.

I've been trying to re-examine the appearances of surfaces with regard to diffuse, reflection/specular. I think sometimes it's confusing that we mentally seperate light and surface properties as such. In Poser we think of reflection in terms of mirrors, metal and water. But in a way what we're simulating is all reflected light (that light that eventually reaches our eyes anyway) - that's how I look at it. The difference is the way in which and how much of that light is reflected by a surface. This gets incredibly complex in the case of skin.

My understanding isn't particularly scientific but it is based on obsevation. I'm very aware of the relationships between colours and contrasts in tones. That's why I know it's very easy to be decieved by what you're looking at. Take a colour picker over the surface of a photo in an image editor and you'll see some interesting colours in shadows and directly lit areas. You have to wonder what's influencing some of that colour - local surface colour or environmental light.

In the case of making a diffuse skin texture, I think we need to start deciding what system of simulating surfaces these textures are designed for - simple or complex. We have to be willing to accept that a diffuse map might not work outside the realm of use with SSS and fresnel reflection with environmental lighting. I have some diffuse maps that are virtually pale-grey with a yellowish tint - look like zombie flesh. But used with an SSS colour map and scatter they do a great job.

 

PoserPro2014(Sr4), Win7 x64, display units set to inches.

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