Do you hesitate to color with yellow?
A lot of people do.
In traditional Copic blending, most colorers have been taught to shade with a marker that is two to three digits higher than your main marker color.
So Y15 would be shaded with Y17 or Y18 and YR12 might be shaded with YR14 or YR15.
But anyone with at least one working eyeball can tell that this simply doesn't work for yellows and light oranges.
That's because there's more to shade than darkness.
Let me repeat that for you- there is more to shade than simply coloring something with a slightly darker marker.
When you step up a marker number in Copics, what you're getting is a more saturated version of the same color. Saturation refers to the strength or the value of a color. To put it in really simple terms- Y15 and Y17 are the same exact ink, the only difference is that Y15 has been "watered down" or diluted with more colorless blender solvent.
So a higher Copic is MORE saturated, meaning it has more pure ink color in the mixture.