This tutorial will show you how to add color to a black and white painting while avoiding a muddy appearance by using gradient maps.
What is a gradient map?
Gradient maps are effects that "map" a darkness value to a color. For example, if we used a rainbow gradient map, then a 50% black pixel might become green, while an 100% black pixel might become purple.
Why do we need gradient maps?
Let's take this black and white painting as an example.
If I add color to this using a blending layer on "hard light" mode, this is the result:
It's not bad! But the tone of the image is definitely muddy. The shadows don't appear very vivid because they are only composed of a single tone.
In real life, shadows are made up of many colors, especially on the boundary between light and dark. Often, the boundary between a shadow and a bright area will appear to be a different color altogether.
What do gradient maps have to do with this?
By using gradient maps, we can add these "boundary colors" to our black and white image.
In the menu, navigate to Layer > New Color Correction Layer > Gradation map, then select the gradient of your choosing to apply to your black and white image.
I prefer to use this sunset-like gradient built into Clip Studio Paint, because it's similar to the way light behaves in real life.
After creating the gradient map layer, adjust the opacity and blending mode to your liking. Here it is on 100% "pin light":
Look how the shadows have become cooler, while the boundary between dark colors and light colors is slightly reddish! And you didn't even have to do anything.
Now, when we add color, it appears more vivid than before:
Further uses for gradation
Just adding a few gradients on the side of the face can increase the ambiance of an image greatly.
If you add a layer that looks like this:
...and set it to 25% additive light, you get this!
While this method is quite fast and easy, in my opinion, nothing beats learning how to create this effect with your own hands.
However, gradation maps and using gradients for color adjustment is a very convenient way to block out colors for illustration, especially if you may not have time to explore many different palettes. If it sounds good to you, give it a try!