Hello,
Sorry to hear you are having issues. Is the issue appear on WB official theme such as Diamond or Acrylic 7?

Thank you,
Basj,
Stardock Community Assistant.

I checked and on my system All MS Office pack including Outlook Classic does not get skin by Windowblinds. But, If you use a Windowblinds theme which changed Windows system color, it will also effect all MS Office pack including Outlook, since they will use system color. 

It is weird, when you said it also have the same result when you apply Diamond. This is what I get while using Diamond.

Thank you,

Basj,
Stardock Community Assistant

Still I don't see the issue refer screenshot below.

Perhaps there conflicting application add on that causing conflict with WB. Would like to suggest to set outlook to be ignore by WB. Please follow these steps below.

Thank you,

Basj,
Stardock Community Assistant