by MadHatter

Hello and welcome to my tones tutorial... you know, solids are fun, and tones are just like solids. Just remember that a good work needs time and patience... ;)   

First of all, be sure to have the lineart on the Layer FG. To unify it there, select the Layer FG then click twice on the Copy button to get Layer Unify and drag a rectangle all over the picture. Now select the Layer BG and start the coloring. [lineart on the FG level, coloring on the BG level = no need to mask the lineart to avoid smudges/color bleedings. You phisically won't color over the lineart.]  


[1] First of all, fill the whole surface you want to color - the hair, in this case - with a base color, using solids. Then fix a Light Source: I chose to put it in the top right corner. 
Starting from the base color, choose at least 3 darker values that you'll use to make the shadows; 3 is the lowest number of colors you need to make a nice shading... of course, the more, the better. :)
To get a quick darker value of a color, just select it and click on the Darken button under the palette window: it substract 10 points for each one of the RGB channels - in other words, it desatures the color, moving it toward the grey area of the spectrum, so the color becomes darker [same process, inverted effect if you use the Lighten button]. Since the process is automatic, sometimes you'd have to adjust the settings to make the color less "dirty", especially if you're using the Darken button.
Usually I click twice [-20 points] from values to values: base color >> 1st darker value [-20 pt from the base color] >> 2nd darker value [-40 pt from the base color] and so on.

When you have chosen your darker values, pick the first and [2] make a quick shading on the hair, according to the Light Source. 
Now, you have to blend the shadow areas with the base color, using tones.

Basically, tones are a pattern of little dots in a predefinited area. You can change the number/position of the dots setting the opacity >> it's the grey bar called "A" under the three RGB channels on the left of the palette. The more the number is high, the more the number of dots raises, darkening the pattern.
There are some different levels of "darkness", from 1 [which is not "white" but the first level of tones] to 255 [all-solid color]; you can also try to overlap different level of tones to make new and different patterns.

[3] Blend the solid shadow with the base color, using a mid value of tones. [around 70/95]


[4] Add some darker values of tones to make the transition between shadow and base color more "faded". Once you're done with it, pick up the second darker value of the base color and start the second solid shading.

The process is the same as before: [5] do a quick shading with solids; [6-7] fade the transition between solids with different values of tones; [8] stress the solid shading with another darker solid color; [9] fade the transition between solids with tones again... and so on, depending on how many colors you have chosen for the shadows.


Now, the highlights. Like what you've done for the shadows, pick up the base color and make it lighter with the Lighten tool. You need at least 2 lighter values of the base color to paint the highlights.
[10] Do a quick highlighting with the first lighter color you made. Then [11] fade the transition between solids with tones, then [12] stress the highlights with the second lighter color. 

At this point, the coloring is almost done. You can add the last details with some touches of solid colors.

This is the final hair coloring; I did the same process on the rest of the face too. Usually the skin is easy to color, since you can use the Hadairo palette, without the need of darken and lighten the base color to get shadows and highlights.

On the top there are all the values of colors I used for the hair: 1 is the base color, 2/3/4 are the shadows, 5 is another color I picked up to make the last details and contrasts on the shading [it's a blueish brown, and the hair are orange >> blue and orange are complementary colors, such as green/red and yellow/purple. Complementary colors tend to contrast each other if they're put close together] H1 and H2 are the highlights.

Down here: the final version of the pic, at real dimensions.