Weird Issue with Custom Colors

I've added a panel and a textbox to my form. When I go into the Properties window for a particular control, there is a "background color" option in there. I can change the color using the "Web" or "System" tab, but the CUSTOM tab isn't working for me. Either that or I'm just having a MOMENT.

Instead of a place to key in my color values or select new ones, I just see this: (attached). Clicking on one of the white cells doesn't enable another custom window either....strange.

If you right-click one of the empty cells at the bottom then you should be able to create a custom colour.