Colors> Image Color Adjustments> Hue / Saturation...
This adjustment is used to change the Hue, Saturation and Brightness of the colors of the design. It also has an option to apply the adjustments to Primary color only. By enabling the Random variation, it will adjust the colors automatically in random ways.

Original design (left), same design after changing hue, saturation and lightness (right)
View tutorial on Changing colors in design using Hue/Saturation