Well, I use glazes of paint. For skin I use the GW glazes (more because I happen to have them rather than because they're anything special). The only real benefit to the pre-made glazes is you don't have to worry about the consistency. Still, when I use the GW glazes I further thin them roughly 50/50 GW glaze and water. Ink is another options, as long as it doesn't give you too satin a finish. But I'd thin that too. Just don't do a wash, since you don't want it to go all over. I start the brush stroke a little below the eye (maybe 2/3 the way up the cheek) and the push away from the top and into the shadows. With the nose, start at the top and push down and under. Build up the color over several layers. I use maybe 3-5, it just depends on how thin or thick your glaze is. Afterwards you may need to go in and redo the skin highlights, check to see if it's needed. If you're making your own glazes from regular paint, make sure to use something like Vallejo Glaze Medium (or one from another brand). This will help the paint react well when it's mixed with a large amount of water.
Here's an example I did a while ago. This is a 90mm figure, so about twice the size of your project... but it's a lot easier to see what I'm going for. The middle image is before the glazes and the far right image is after. Notice the color change on the cheeks and nose.
I attached two images from another project, this time a 54mm face. The first image set is before the glazes and the second image set is after the glazes. There's a bit more going on here, red on the cheeks, nose and bottom of the ear. Purple in the lower part of the cheeks and under the eyes to strengthen the shadows. Then blue on the lower part of the face to create the look of stubble. None of the colors are that extreme, just tinting the existing work. You
don't want the cheeks and nose to be bright red, just a subtle color shift. Your guy's ears are covered up and so is the lower part of his face, so no need to worry about them.
Keep in mind that there's nothing wrong with the faces before glazing. You're welcome to skip that step if you want. But I think it adds a little more life to the face and is a nice final touch. You can do the same thing on his body, by the way. You could add a little red tint to his knuckles and elbows.
