You can easily fulfil your requirements with a couple of lines of CSS:
In order to keep the right looks of RadColorPicker, I have used visibility: hidden
for the increase / decrease buttons instead of display: none
as I did with the footer of the control, where the "Apply" button (.rcpApplyButton) is rendered. In any case, you may play with these properties the way you find best for your project.
the Telerik team