Basic understanding of .mtl File in OpenGl ("Source : https://en.wikipedia.org/wiki/Wavefront_.obj_file")
.Mtl File Normalization
A single .mtl file may define multiple materials. Materials are defined one after another in the file, each starting with the newmtl command:
newmtl Colored
The ambient color of the material is declared using Ka. Color definitions are in RGB where each channel's value is between 0 and 1. Ka 1.000 1.000 1.000 # white
Similarly, the diffuse color is declared using Kd. Kd 1.000 1.000 1.000 # white
The specular color is declared using Ks, and weighted using the specular exponent Ns. Ks 0.000 0.000 0.000 # black (off) Ns 10.000 # ranges between 0 and 1000
understanding of this three Light Color https://qph.ec.quoracdn.net/main-qimg-dbc0172ecc9127a3a6b36c4d7f634277.webp
Materials can be transparent. This is referred to as being dissolved. Unlike real transparency, the result does not depend upon the thickness of the object. A value of 1.0 for "d" is the default and means fully opaque, as does a value of 0.0 for "Tr".
d 0.9 # some implementations use 'd' Tr 0.1 # others use 'Tr' (inverted: Tr = 1 - d)