Chris: Well, bless you for coming back again.
I really did struggle with this portrait, and changing so much color in the piece worried me for a long while into the process.
In the end it was the values that made the difference. Because I was working in monochrome in the underpainting, I had a value scale for the dresses. I made a nine value scale with the blue colors as I saw them in the dresses. I then did the same with three hue variations of yellow comparing each value with the corresponding value in the blue to capture a similar "intensity" or chroma between the yellow and the blue. I selected one that worked the best and went with it. I also specifically looked for areas where the blue was playing into the flesh tones and warmed them up instead.
Another thing that gave me some challenges was that in my original reference, the girls are not together. I had to put them together and get relative sizes as Peyton is two years younger than her sister and their sizes in the reference were the same. I also had to figure out shadow interplay between the girls as they needed to look like there were right there together. It was tricky.