I think keep it as is, but use it as an opportunity to explain the difference, perhaps? I imagine this would be great for scientifically-minded kids to learn from.
I actually do explain the difference if you explore deep enough into the app (maybe it's too difficult to find) - if you click on the color reference button in the gameplay so that the color palette pops up, there's a button at the bottom called "Learn more about colors" that brings you to a multi-page explanation on the additive vs subtractive color models.
