Use a long tap to color faster. Tap and hold a cell, then drag your finger across neighboring cells.
For a more accurate approach, you can enable the Magnifying Glass in the settings of the app.
You can also use boosters:
– Color Splash colors multiple neighboring cells with any numbers.
– Magic Wand allows you to color multiple neighboring cells with the same number with one tap.
To use boosters, swipe the palette to the right, select one of the boosters, and tap any cell with a number on the artwork.