There is a Setting in Microsoft Outlook 2010 to configure how shading is applied to the form fields of a message. To access this setting via the GUI, start Outlook, click New E-mail, then from the File menu select Options, Editor Options, Advanced, then under the Display section, select the appropriate value from the Field shading drop-down list box. The available options are Never, Always, and the default value, When Selected.
Unfortunately, the current value is stored within a large binary blob in the registry. It does not appear to be possible to change this value via group policy (without using a group policy preference to blat the entire blob, which isn't desirable).
However, you can programmatically adjust the setting by running the following PowerShell code under the context of the current user (while Outlook is closed). The script modifies the 321st byte of the registry blob from hexadecimal 30 to hexadecimal 20, thereby changing the setting from When Selected to Never.
There are several ways to modify this setting across the enterprise, but I think the best approach is to wrap the code into an MSI and leverage Active Setup to apply the change at the next user logon.
$settings = (get-itemproperty -path HKCU:Software\Microsoft\Office\14.0\Word\Data -name SettingsWordMail).SettingsWordMail $settings = 32 set-itemproperty -path HKCU:Software\Microsoft\Office\14.0\Word\Data -name SettingsWordMail -value $settings