I don't adhere to a particular color theory, more like multiple scraps of good advice I have picked up over the years! But I will say I didn't get the importance of color theory until I read James Gurney's Color and Light: A Guide for the Realist Painter. If you want some practical color theory concepts that you can actually use in your artwork, I highly recommend this book. It has changed my otherwise dismissive view of color theory as Gurney manages to appeal to artists rather than making them want to stick their fingers in their ears!
In addition to color, I do pay attention to contrast and value, and color overtones (red, yellow, blue). At the start of a piece, I am interested in good composition and design.
I also believe that learning about color mixing by trial and error is very useful. When you try to put a pale thick blue paint with a thin yellow, certain things are going to happen and it's good to know what those are before you waste a ton of paint! Color theory is helpful, but it's the pigment that has the final say. Take some time to mix your favorite paints with each other and see what happens. Those charts you can make showing color mixes are actually a very useful reference tool and are worth taking the time to build.
Color can be used in so many interesting ways and it can be enlightening to experiment. For example, I was sketching in the woods the other day and decided to do some small watercolors of trees using any color except brown. I got some wonderful bark texture from shades of purple and gold and turquoise, really unexpected and beautiful. That sort of playing around on a small scale can really improve your larger work and provide you with some new ways of looking at familiar subjects as well.
And in any art museum, portraits are everywhere: in every style, color, and size, from every country and created by every type of artist.
In a portrait's brushstrokes we find a path connecting us to another human on a timeless level.
Da Vinci's Mona Lisa, van Gogh and Rembrandt's many self-portraits, these are just a few of the well-known portraits that have come down to us through the ages. Their popularity is testimony to the power and value of capturing personality, character, and aspect, on canvas.
Oil paint captures the living qualities of the human face and body like no other medium. Skillfully handled, the portrait transcends technique and draws the viewer in, and a single artist creates a treasure for us all.