I didn't have a reveal button in the upper right hand corner of my Keynote Colors window. If you don't either, here's what worked for me:
1. First, verify and repair permissions using Disk Utility. Go to your Applications folder, choose Utilities, then open Disk Utility. To start the repair process, click "Verify Permissions."
2. Once that's done, quit Keynote if it's running.
3. Find your Keynote Preferences. To do so, select Finder in your Dock. Then hold down the Option key on your keyboard and select the Go menu at the top of your screen, which will put a "Library" icon between the Home and Computer icons in the menu list. Select "Library".
4. From within your user Library, select the Preferences folder.
5. Find your Keynote preferences. Depending on when you installed Keynote, the file will be named something like "com.apple.iWork.Keynote.plist" or "com.apple.Keynote.plist". It could be in an "iWork" folder. (BTW, you're NOT looking for any file that ends in ".lockfile".) You might be able to throw away this entire file and get good results. However, I chose to get a little more specific:
6. Right-click (or Ctrl button + click) on the preferences file you found. Select "Open With". If it's installed, the default application should be "Property List Editor.app", which is what you want. Use it to open your .plist file.
(If Property List Editor.app doesn't appear, check to see if you have it installed, which will probably be here: yourHardDriveName/Developer/Applications/Utilities/Property List Editor.app.
- If you don't see this folder or this application, it should be available to you as part of your Mac OS X installation software. Alternatively, it may be auto-installed if you upgrade to the latest version of OS X Mountain Lion if you haven't already.
7. Your Keynote .plist file is now open. Here's where my memory gets a bit fuzzy because I tried deleting multiple preferences until I got the right ones. However, since they're just preferences, you should be able to delete them without adversely affecting your application's ability to function. To delete, I used the "Delete Item" button in the window's toolbar.
I deleted all preferences that started with "NSColor" except the following:
I also deleted an item either starting with (or nested within) one of the preferences that started with "Insp". Here's what's left:
Nested within each of these is simply an "Item 1". If you see any other nested items, consider deleting them.
8. Save your edited .plist.
9. Open Keynote and open your Colors window. You should be seeing your color options restored.
If you're not, there may be something more going on, which is also fixable. I discovered the above solution after de-installing and re-installing all my iWork applications, cleaning out older/non-functioning applications, and throwing away as many leftover preferences files as I could recognize.
Incidentally, the above procedure did not bring back the Colors window reveal button. Getting that back may require additional steps, which I didn't try to discover.