This illustration has a "watercolor feel" to it. The white paper was left untouched by the pencils to create the highlights. Colored pencils are wax based. They do not blend like pastels and graphite pencils. The various colors and hues are created by layers. The pencils are somewhat transparent, so the gradual layers form shapes and shadows. I use all vertical lines as I'm drawing each layer (except for hair). If you were to look very closely at this illustration, you'd be able to see all the lines in their skin and clothing. On later illustrations, I use a clear "waxed" pencil to burnish, blend the colors together. That way, no lines are visible. It's a matter of preference whether to blend together or leave the lines. I like the smooth look in skin after I blend all the layers together, but some people prefer seeing all of the lines that create an artistic look.
The photo this was drawn from had a chair and various toys in the background. I wanted Kristen and Heather to be the focal point, so I omitted everything else. At first, I had just a cream colored background. That made the girls look like they were floating in some unknown space. So I added a border behind them, resembling the edge of the floor, wall trim and wall. I didn't put too much detail in any of the background. I wanted the viewers eyes to stay on the girls. I also added a shadow under Heather to make it more noticeable that she was on the floor and again, not floating in space.
The girls are two years apart and were inseparable. Heather was a shy little girl and would use Kristen as a body shield and security blanket when entering a new place. Kristen was daring and trusting and was always ready for a new adventure. I remember once I had joined a new gym that had a children's daycare. The girls were four and two (about the same age as in this picture.) Heather was terrified to be left with strangers. I told Heather that I was only going to be gone a short time and she could play with Kristen and all of the toys in the room. She said "OK" and held Kristen in front of her and the two of them entered the room. She stuck to Kristen the entire time. I thought it was sweet that Heather felt more confidant and secure with her baby sister by her side. (or in front of her, in this case). The two girls have always been close. In college, they attended different schools, but in the same town, so they shared a house with two other girls. Later, they remained living together as they began their new careers. They now are living their separate lives in different cities, but they will always be close in their hearts.