In Edgar Degas's painting "Dancers Backstage," the artist primarily uses color contrast to focus on the main ballerina and to create visual interest throughout the composition. While some colors may be similar to the background, Degas effectively highlights the dancers, particularly the main figures, by employing contrasting colors that draw attention to them.
For example, the use of warmer tones for the ballerinas contrasts with cooler tones in the background, making them stand out. This technique helps to emphasize the movement and grace of the dancers while also giving depth to the scene. Therefore, the most accurate response to your question would be that he created color contrast to focus on the main ballerina.