PBR grass vs asphalt albedo/base color value?
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Does anyone know why basically any base color/albedo gude says asphalts including old/worn ones base color should be darker than 
any random grass/ foliage albedo and yet I see it every day that a grass is usually darker through a day until late afternoon at least toward the sun only where we se lots of grass translucency/ SSS and it may look brighter ? And no physical property even in offline renders could make it look otherwize? Thats sRGB 80 in top right corner . A recommended one for old dusty asphalt .
any random grass/ foliage albedo and yet I see it every day that a grass is usually darker through a day until late afternoon at least toward the sun only where we se lots of grass translucency/ SSS and it may look brighter ? And no physical property even in offline renders could make it look otherwize? Thats sRGB 80 in top right corner . A recommended one for old dusty asphalt .Sun is behind in this photo at 48 degree elevation so it's not that lots of highlight spot /specular lobe here.
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Now let's assume for the sake of argument that really worn asphalt is not just an omission and speculate a bit: With the sun in the back like in the picture, the rougher the material, the more "direct" sunlight will be reflected back to you. The (I assume) less rough grass/foliage will reflect more sunlight back to you when at the right angle, but most bits will be oriented differently and there are lots of holes in the coverage and shadows. The same goes for the bigger light of the sky, just less easy to visualize.
If we look at the flowers in the foreground, the brightest bits seem also the most saturated, and saturation can play tricks on us regarding how bright we perceive something to be, but I'd say there are both more bright and more dark spots in there than on the asphalt. With the brightness of the albedos given in the upper right corner being almost the same, that sort of makes sense. As for the grass in the distance, it all smushes together. We can make out some brighter waves that might be flowers or the sun or sky reflecting in more blades of grass, but we probably look at more shadowed areas than we realize in that case, too, even with the sun in our back.
For a direct comparison, you could pin down a blade of grass to the asphalt and see how it reacts to light.
Ohh.. indeed.. just was (double) checking.. see some technical paper from the American Concrete Pavement Association and also the original term via Wikipedia: Albedo (from Latin albedo 'whiteness') is the fraction of sunlight that is diffusely reflected by a body.
..so the albedo-"color" is choosen darker ( if i'm not mistaken ) to match better the final result.
As such...
if your light source (the sun) is on the other side of the patch of grass from you, any light going in has a relatively low chance of coming out in the direction of the viewer (you). Since less light == more dark, the grass looks dark
GGX (etc) cannot replicate this behaviour so you need to fudge things
The color of asphalt is largely a function of the kind of stones used and how much crap is ground into it - it'll tend to take on the color of whatever dust and pollutants are prevalent in the area with things like how much rain it gets affecting how much crap accumulates.
GGX can cope with this but since it's really complicated to science it out you're better off just eyeballing it
Just don’t go insane with values, until you have a solid base established.
220/255 for white paint, 50/255 for black paint. 187/255 for mid gray. Etc. Adjust your lighting and camera exposure so those look good, then you have a decent baseline to work within.