Adobe Color Lava

Of the three apps, Color Lava is my favorite to fiddle with, but like all of them not as useful as one would wish. You create color palettes by mixing primaries, paintlike, with your finger. The longer you paint two colors together, the more they combine. The gray square in the upper left corner is "water"; you dip your finger in it to use it. Tapping the camera icon brings up your photos if you need to search for a reference image. If you're connected to Photoshop, any selected swatch becomes the currently selected color.