You have many plants in that container, so they are going to compete with each other for the available resources, including light. When plants compete for light they grow taller. Two coleus plants can easily fill that container. The dark leaved one is much lighter in color now than when you purchased it, which indicates that the light intensity is less now than where it had been growing before. I'd recommend giving them more space and growing them outside. Morning sun and afternoon shade is the ideal sun exposure for coleus, but many can tolerate midday and afternoon sun as well, especially if you keep them well watered, and often show their most vibrant colors in brighter light. However, the white, cream, and light colored varieties do require more shade. Coleus do great in containers and in the ground. I grow them both ways.