Find and replace color
Sometimes you decide to change a color after you've used it extensively, but going through detailed colorings to find all instances can be too time consuming. Plus if you've used shading or other effects, you lose it if you have to erase and refill. It would be nice to be able to click a color on the palette, hit "replace with" and then pick a new shade. You could also choose "keep effects" if desired.
I love the grayscale images, but on occations I want to flood with a dark colour then work on the details. If I do this its hard or impossible to see the outlines. If I could flood fill with a light colour and then when complete I can tap replace Colour x with colour Y (at pixel level), Boom, job done.
You should create the option to select a colour (with the eye dropper or palette) and then choose another colour to replace all of the original colour in your picture.
Select a color on the pallet and then click a color in the drawing and have the selected color in the pallet replace all of the color that was clicked in the doodle