Paper is a very well done app. I like the description of how they went the extra mile to make color selection natural. Spring for the mixer in-store purchase, if only to see their interface in action.

If Everyone Else Is Wrong, Why Bother Innovating?

So why was it worth a year of development and brainstorming to fix this intractable color-mixing problem? The FiftyThree team says it’s about giving your big features–in their case, the watercolor brush, the marker, the pencil–room to grow and improve. Without fixing the color dilemma, the rest of the app couldn’t improve.