I want something like the properties' color drop down in Visual Studio. I can't seem to find any tools for this though.
I'm afraid you won't find that "natively" on .NET. The PropertyGrid control displays its values based on Editors classes specifically designed for presenting/editing each property type in its own manner inside of it, and that's not what you need. Besides this, you will only find the ColorDialog, which is not what you want - I guess.
You will need to get and reference a custom control from what is available on the web. Here are some free options I've found on a quick search:
http://www.codeproject.com/Articles/1484/NET-Color-Picker-Controls http://www.codeproject.com/Articles/8305/The-ColorPicker-WinForms-Control-Revisited
PS: If you are working on a commercial app that demands a lot from the UI, you should consider buying a full control/component set for Winforms, which brings a lot of nice controls (ColorPicker is one of them). From my own experience, it is worth.