It is related to the number and size of cyan balls in your screen. If you have enough and done the red level, you've beaten the second level.
Viewing post in Yet another color merging game jam comments
Well, the problem is, when you hit any cyan ball, you need to start from scratch. I got to the point where I had every possible upgrade; I tried several times to survive the cyan level and always failed.
Now the save seems to be wiped, so need to start again :(
UPD: tried again. Still cannot complete, still frustrated.