Hmmm, I sure don't remember installing Virtuemart on this site, yet I discovered a VM plugin. Interestingly, it wasn't enabled, yet it still managed to intercept that call to the view order page and throw an error. I would have thought that a disabled plugin shouldn't be able to mess with your site.
I have found out how to amend the colors on the orders page - in particular the "No orders found" box. However, the box below that just says "Orders" with a big red cancel button. Clicking that takes you to a screen which I assume is the customer dashboard (I still have yet to set up most of the front end interaction). However, the Cancel button is not especially intuitive - maybe the screen looks like this for a genuine, live order, I'm not sure. IMHO, it should say something like "Go to your dashboard" with an arrow. I saw how to change the icon, but not the wording.