An eyedropper control beside the color well lets you pick a color in use in the Motion Canvas. By choosing from colors in your scene you ensure that elements remain in the same palette, creating a more cohesive and integrated design.
Pick a color using the eyedropper
In the Inspector, click the eyedropper for the color parameter you want to set.
The pointer turns into an eyedropper.
Click a color in the Canvas.
That color is assigned to the color well.