[SDFormat->MJCF] Material specular and emissive is a scalar not a color

[ahcorde]

SDf defines material specular and emissive as Color (r, g, b, a) but MJCF defines this as a scalar.

If, for example, you have a specular of [0.9, 0, 0], I would expect a red highlight, but this would result in gray.

Related comment #18 (comment)