Here's a simple C# colour picker I've created. It's derived from a combobox with a simple override on the OnDrawItem() method. It looks like this:
And you can find it over on my GitHub page.
This contains no error handling, and is simple as it can be, so use it and your own peril. It's not going to make your computer explode, but you know what I mean. Any problems, feed etc drop me a line.