It wasn’t the colour, you would burn little bubbles into the disk. The bubbles would deflect a laser and flat parts would not. This would give the 0 or 1 bits.
There were CD- and CD+ versions. I don’t know which is which but one would create a divot, and the other would create a bubble. Either way the laser is diverted away from the sensor.
Did I write and publish it this while sleepwalking or something?