Material color is darker in Kd in .mtl file than it is in blender I'm using Cycles Render and exporting my model as .obj and .mtl files. I have a simple green diffuse material, but in the .mtl file, the color becomes a much darker green. The viewport color and the material color are the same (I know that the wavefront obj/mtl files use the viewport color).

It SHOULD be Kd 0.121568 0.364705 0.149019 (hex #1F5D26)

but it's exporting as Kd 0.010962 0.087569 0.015506 (hex #031604  )

Why is this happening?



.mtl file:

newmtl PineTree.001
Ns 96.078431
Ka 1.000000 1.000000 1.000000
Kd 0.010962 0.087569 0.015506
Ks 0.500000 0.500000 0.500000
Ke 0.000000 0.000000 0.000000
Ni 1.000000
d 1.000000
illum 2




Blender material:
Like Troy said it's a color management convertion.
In cycles colors aren't bounded to 0/1 range, this is scene referred datas.
In .mtl files colors are stored in a 0/1 range, the display referred datas.
Look the Wiki for description of Wavefront .obj, scroll down to the section "Material template library" and subsection "Basic materials"
It's said that : "Color definitions are in RGB where each channel's value is between 0 and 1."

So with that in mind you couldn't expect a 1/1 between Cycles internal values and exported bounded values. Plus I don't know if you're aware that Hex values are gamma corrected in Blender.
It looks like there is a transfere curve, I guess an EOTF curve, see here for more details : the-importance-of-terminology-and-srgb-uncertainty, the whole article is worth reading but there is a section about the sRGB EOTF transfer curve.