How to fix acidic smell from fridge/freezer?
The tray under your refrigerator is there to catch condensation is it goes through its normal operating cycles.

The water might building up and overflowing or other there is direct condensation in the other areas. The color and smell is from the typical things that grow in stagnant water (mold, etc) and can be cleaned up with the same normal cleaners. It probably got a foothold in the tray, and if the tray is not overflowing, then also got to the other wet locations easily from the tray colony.

This is then a typical household cleaning issue that you can approach as normal.

Things you can do to improve the situation: some water in the tray is normal so it's not an option to not have water there but we can make it unfriendly to the little buggies: put a few drops of chlorine bleach in the tray once in a while to keep it non-life supporting. Since there is an issue outside the tray, this indicates that your house might have a lot of moisture. If so, a (portable) dehumidifier can bring down the humidity to something more reasonable