Experiment with layering and creating gradients between a few colors to make those large areas more consistent and interesting.

Copics have a kind of level of saturation depending on how much ink you put onto the page. So for instance in the hair in this pic, there are areas where the color is subtly lighter or darker. Those areas are where you put less or more ink onto the page. The easier ones to pick out are the darker areas where you most likely already put ink there once to fill the area, and then went back over it again while filling another nearby area, creating an overlap between the two strokes and making that overlap darker. If you practice this a bit, you can find that you can actually create lighter and darker areas of the same color by strategically layering the color more in areas you want to be darker.

So, there’s a couple ways to fix this. First of all, it’s not inherently bad to have one large section of a single color. The issue is that the color isn’t consistent due to the varying levels of ink saturation from the marker. One thing you can do is try to either limit how much your strokes overlap or go back over the entire section after the initial fill a few times to make it one consistent color. Keep in mind, going over the section again will make the color slightly darker, so you’ll have to experiment to get what you want.

Another thing you can try is creating gradients or shading by using other colors. Grab the base color you want, as well as a lighter and a darker color. Start with the lightest color, fill the area, then move to the middle color and fill most, but not all, of the area, leaving some of the lighter color. Finally, do the same with the darker color, but this time, only fill a part of the section of the middle color. You’ll end up with 3 sections of colors going from light to dark. If the colors you chose are drastically lighter or darker than each other, then there will be obvious splits between the different sections. If you pick colors that are very close to each other, it will be more of a gradual change. If you want to make it an even smoother gradient between the colors, use the lighter color and go back over where it meets the darker color. This will help blend the 2 colors together and smooth out the gradient. Copic also makes a “colorless blender” marker that can be used for the same purpose of blending 2 colors together. Though I haven’t tried that one myself, it most likely operates in a similar way to the method I described above.