This face is coming right along nicely. See the photos below.
It's time to start lifting the nose up off the paper. It is done by shading the sides of the nose and paying attention to the highlights along the bridge and around the nostrils.
As I began the nose I noticed his eyes didn't look quite right. I got out my mylar sheet and sure enough the fold above the eye on the right was turned wrong. You can see the correction by comparing the second photo with the third.
Once the eye was right I used Peach to begin pushing up the side of the nose. I felt like I needed to "anchor" the nose so I started the cheek on the shadow side of the face. I slowly built up the cheek color by using at least one color from each skin tone level working up the value scale all the way to level six which includes Dark Umber and Tuscan red. As I worked the cheek I worked the value level of the nose along with it. To develop the cast shadow on the cheek along the edge of the nose I had to go to black because that side of the face is in such deep shadow. I rarely go that dark in a portrait.
I used my mylar sheet to check the shape of the nostrils. Though they are tiny but they must be the right shape to make the nose look right.
It's important to save the little white highlights on the nose tip by working color around them. Those highlights help move the nose tip forward and give depth to the face. The nose tip generally tends to be shaped like a partial ball and should be shaded like the ones all artists practice when first learning to render a sphere. The nose bridge should be thought of as a cylinder and shaded much like those cylinder lessons we all did when we were learning to draw.
You can see in the last photo how the nose curves and turns as the shading is developed. Apply the lessons you learned in rending curved surfaces when you first learned to draw. The important thing to remember is that color does not matter nearly as much as value. If you have the value level right the color choice is secondary. The secret is to work in light color washes if you need to adjust the color you can easily do it.