by lithy
Ok, so this was your scenario?Yellow is cured, but still lots of yellow cubes on the board.
Red, blue, and black were not on the board at all when the second epidemic was drawn. You were still putting any colors of these cubes out when cities were infected right?
I suppose this is possible, though unlikely.
The official FAQ says that if you find all 4 cures before the second epidemic (which is also possible, though unlikely), you use the one with the most cubes. This doesn't really apply to you.
The card says if more than one disease is eligible, then you choose. In your case 3 diseases (assuming you played eradication correctly) are eligible since they are uncured and have the same number of cubes (0).
So you should pick red, blue, or black as CoDa-403a.