I don't do fully digital piece to often and when I do, the approach can be quite different from my usual line based artwork so I thought I share the progress in video. This portrait took me roughly 40 minutes with no prior planning, mostly driven by the feeling, so I stalled few seconds time to time. (So spare with on that.) ^-^;
The major difference in painting and coloring here is constructing the subject in solid shape while my pencil work is based on capturing the subject in lines. When I don't have a line to reference, I start with defining the silhouette of an object and after establishing basic shape, I work with new transparent layer to multiply/overlay (-Shade/Luminosity in SAI) colors to add shading. I keep the brush setting pretty much static except at the beginning where I'm adjusting the brush till I reach the optimal setting. Since I'm working on new layer, there is no real color "mixing" happening while I paint for the most part, however the brush setting does have a blending parameter as a default setting. It's about adding new layer to add shadow or brightness and then merging it with the main layer. I repeat the process to gradually defining details and in the later stage I would go in the main layer to blend the rough areas. I tried to incorporate the angular shape created during the process and use that as a shape that defines the portrait. (rather than smoothing them out.)
For the image posted on Instagram, I brought it to Photoshop to fix the angle and to composite (for effect) but there is no further painting job applied. In compositing, I imported the original image to boost the contrast and then applied my own texture over it.
Layer Structure of effect. (From bottom to top)
1 - Grey Background
2 - Image imported from SAI (the original)
3 - Duplicate of an original, setting the layer effect to "COLOR BURN" setting opacity to 50%. I did this to boost the saturation and contrast, exactly what Color Burn does.
4 - This layer was pre-composite to lift the overall brightness while leaving the contrast.
5 - Sepia texture, supplementary layer to further enrich the image.
6 - Merge layer of all layers to create Chromatic Abbreviation effect. (New merged layer, so that I don't mess up the layer below)
For the final effect I've applied chromatic abbreviation effect to go a bit fancy. (*chromatic abbreviation is a type of blur effect, kinda like an old vacuum tube TV with RGB calibration being off/shifted. In any case it's a bit of an overused effect. ^-^;)
*** I couldn't add a sound because it takes too much rendering time on After Effect on my prehistoric laptop. (Apology)