Basically, a toggle that makes it so when the board no longer contains a certain color, the game will never pull that color again for your pills. This is similar to games like Puzzle Bobble, for example.
I considered this earlier in development but never implemented it because I thought the chances of fully removing all of a certain colour (viruses and pill segments) was low, but I could potentially add a setting for this in a future update. If I were to add this, do you think when all viruses of a certain colour are killed, each remaining pill segment of the same colour should auto-vanish along with them, or should they stay and the smart RNG only kicks in once every pill of that colour gets eliminated in addition to the viruses?