
Olly S. answered 05/20/20
Illustrator and Concept Art Generalist
Dull coloration can also be part of which paint you are using. Student grade paints are typically more dull than professional grade paints, and most lines of paint have a distinction between student grade and professional grade. The real difference being professional grade paints take more premium ingredients to make, and tend to come out more saturated.
Another thing that might help is cleaning or rinsing your brush before you start to mix more colors. Pigment residue builds up on the brushes over time and can muddy your other pigments.
Dullness (reading in this context as blandness) can also be part of not planning values out ahead of time. Doing a thumbnail of your piece in greyscale can be most helpful in this case!
Messy can also be a stylistic choice! Embrace your messyness, or if making crisp forms is something you want to improve upon, practice! Be kind to yourself and give yourself permission to make something messy, and let it happen. As long as you make an effort to practice, you'll improve!