To include it in my recent post about the HG 1/144 Gundam Caliber, I took out my HG 1/144 Gundam Aerial, which I built several years ago, from storage. To my surprise, the yellow molded parts had turned red.

The cause appears to be a brown panel lining pen.

Luckily, I hadn't applied a top coat, so I quickly disassembled the parts, washed the yellow ones, and touched them up with a gray panel lining pen.

2-1 Gundam Aerial Repair Part 1 | さんぴんちゃ's Gunpla works