UPDATED:
Starting with version 13.2, ASPxColorEdit provides the built-in Custom Color Picker allowing end-users to select custom colors. This allows accomplishing a similar task with less effort and does not require so much extra code. You can try this functionality in the Color Editor - Example online demo.
This example demonstrates how to extend ASPxColorEdit so that a user has the capability to select a custom color. For this purpose, we use the following jQuery plug-in to extend the control:
Color Picker - jQuery plugin