Make color of the Moon closer to reality

If you have ever looked at the Moon through a telescope, you may have
noticed its peculiar color, which is definitely not gray nor white. It's
closer to beige. This patch makes the color of the simulated Moon like
this.

The reference color was taken from a minimally-processed photo I made of
the Moon when it was at elevation of about 65.9° — highest achievable
now at my current location to minimize the effect of the atmospheric
extinction.

data/shaders/planet.frag

@@ -425,6 +425,7 @@ void main()
 	// maximum at 1.0 instead of 0.4.
 	texColor.rgb = vec3(0.4) + 0.6 * texColor.rgb;
     texColor.rgb = pow(texColor.rgb, vec3(2.8));
+	texColor.rgb *= vec3(1., 0.79, 0.57);
 #else
     texColor.rgb = srgbToLinear(texColor.rgb);
 #endif