Orion (The Last Color Study) by Paul Pope w/ colors by David Zissou.
The first two are single gradient layers with orange tints on the line while the second two are those layers combined to mellow out the colors.
I find that by tinting line, whether by reds for heat or blues for coolness, I’m attempting to reproduce an illusion of distance I see in some of my favorite Sumi-e paintings; as objects in a painting are further from the focal point the inkwash becomes lighter; or similarly in watercolor taken from observing mountains in the distance, the colors become distorted and appear purple due to atmospheric perspective. Essentially, a tint can distance the eye from the page where a black line is bold and pops towards the viewer. This is probably most effective with artists who wash their inks out like Paul Pope and Mike Mignola, opposed to just going straight 100% black. Also, this technique is probably more suited for directing the eye in crowd scenes and composing landscapes than a single focused subject like Orion, but it’s an interesting and fun effect to play with.