Thank you very much for your error report.
This has been reported a few times before but we have not yet been able to find a way to reliably reproduce the problem. Moreover, the problem is usually gone after restarting yEd.
May I ask if the problem is reproducible for you? If so, can you give step-by-step instructions to do so? Additionally, it would help us to know on which operating system you are running yEd and which version of Java you are using (see "Help" -> "About" for the latter piece of information).
Finally, let me thank you for offering to produce a screen cast/capture. This will only help if you can demonstrate a reproducible way to trigger the palette problem in your screen cast, though. (We already know how the problem manifests - unfortunately, that does not help with reproducing it.)