I'm on the 12.9 iPad pro 2nd gen.    I load the image attached to try and use as a learning tool.    My goal is to select just the tree and use the brush tool to paint on a color overlay. However Everytime I do this the brush tool affects both the tree and the sky.    My process so far has been.    Open image.    Use in painting to remove some stray black dots.    Use the option in the selection persona to select by color of sky.