[blackle]

I've noticed that adding a colour can make it go from having a solution to not having a solution. Maybe it should try to come up with a solution using fewer colours in that case, since it's not obvious that manually removing a colour will lead to a solution.

[jstrieb]

That's a good observation - the UI is a very thin wrapper around the optimizer.

One fix would be changing the minimum number of chips per color under "advanced options > requirements" to 0.