What does the fourth parameter that 'diffuse_color' takes in Blender 2.9 do? It seems that the diffuse_color definition has changed in Blender at some point as older scripts in which it was defined by the struct with 3 parameters now it requires the struct with 4.
Does anyone know what is the meaning of the fourth parameter?
Diffuse_color take 4 parameters as RGBA
red, green, blue, alpha
mat.diffuse_color = (red_v, grn_v, blu_v, alpha_v)  # viewport color