Just focus on making color choices for the most important parts of the illustration.
Quickly (for just about 15 minutes) use a large soft airbrush to block in colors.On a layer set to overlay above all other artwork, experiment with different color schemes.
Gather reference of great color schemes and environments for inspiration.Duplicate your document and reduce to 72 dpi.I always experiment with color BEFORE I begin working on the final piece.Using reference layers makes coloring much faster, because you can use the magic wand tool to select quick masks of certain areas, without having to switch the layer you are working on.Once finished, you set this Flats layer as a Reference layer in Clip Studio Paint.“Flatting” a piece consists of coloring the basic shapes of the illustration in random, unique colors to differentiate the different elements from each other in order to make quick selections when coloring.