When we burn a CD or DVD we start the laser and burn until we're out of data. When you look at the CD, you can see the data, and where there is empty unburnt space.
I'm sure this is nothing new to most of you.
Through clever coding and firmware manipulation, a burner could be convinced to write
a visual design on the CD. Even make multiple passes with the laser for a different effect. It would be sort of like a radial plotter with a laser pen.
For an EP release or something similar, the disc could be mostly light refracting designs with some data at the beginning.