Sadly there are a very light discolouration patch on the brown disc surface – MODS.

Disc Game for Atari ST Computers.

MODS: The condition of 3.5 Inch disc surfaces is becoming an issue in the 16-bit collecting scene. Nobody expected people to still be booting these games up thirty years later, and, depending on how they've been stored, it is common to find small discolouration patches, white spots, and even mould on the brown surface of the disc. We have had some limited success cleaning light spots from disc surfaces in the past, but often it renders a disc unusable. We won't list games with big mould patches, but games we list with MODS will have a light issue - perhaps only on one of multiple discs - perhaps light enough to still play through, or be gently cleaned, but these games are sold as untested for parts only.