Green and white mold on dry part of onion only. What to do?
Because nothing else is affected, your red onions probably acquired the mold spores before you purchased them. Perhaps they were stored in a humid area that facilitated the rapid growth. 

Hopefully, you didn't store them in the refrigerator. Onions should be stored in a dry area of your kitchen or pantry in a manner that allows for good air circulation. Use a wicker or wire basket rather than than a plastic container.

I see a big red flag in your mentioning storing potatoes in the same container. Potatoes should never be stored in proximity with onions because onions give off a gas which will cause potatoes to spoil. Keep your potatoes in a separate area, preferably dark, and which also permits air to freely circulate.

Regarding what to do with the moldy onions now: wash off the mold and allow the onions to dry, and/or cook with them as soon as possible. After peeling off the outer skins, if the flesh of the onion looks good, with no mold or dark spoiled areas, then I think they'll be safe to use.

If you have too many onions to cook right away and are afraid the mold will progress, slice and/or dice the onions as desired, and blanch them in some boiling water. Then, seal the blanched onions tightly in one or more packages for freezing.