[stomachmonkey]

A CMOS is a mechanical sensor that due to the nature of it's design can be sensitive to the angle and amount of incoming light energy.

There are 3 basic types of materials, diffuse reflective, retro reflective, specular.

They will affect how light energy is dispersed back to the sensor.

Diffuse reflective will scatter / disperse some of the light energy hitting it so less energy hits the sensor than hits the object, think concrete.

Retro reflective will concentrate and amplify energy directly back, think reflective road paint or road signs.

Specular, tends to redirect concentrated light energy, think laser hitting mirror.

So it is entirely possible to have two identically colored but different materials return different results.

It's not the color, it's the material properties of the two different coatings that are effecting what the sensor can interpolate. One may be rougher / smoother than the other.