Hi reedmj
I found this knowledge base article: http://kb.parallels.com/en/6858 in it it states:Note:
This theme is available for Windows XP , Windows Vista and Windows 7 guest operating systems with up to date Parallels Tools installed.
To be able to use this theme, you need to log in to Windows as an administrator.
Could it be possible that you are not logged in as an Administrator when attempting to change the color or your Parallels Tools are not up to date?