In this jam each color that has it's own "color code" is considered a separate color. However, there is an exception to this in the rules. Rule: "Gradients are allowed but no more than 3 objects/sprites/backgrounds in total with a gradient and the two main colors from the gradient count towards the 10 color max.". So basically you can still do shading with gradients but you have to follow that rule. Btw you could also do shading using dithering.