I also got a white screen and had a rough time trying to figure this one out myself.
For me, it was the fact that essentially a 7.5 language pack was in use that dashboard.php couldn't do anything with. If or when I have some free time, I'll just update those language files myself.
General CSS Properties > .t_standard
This group should not have have its own background and colors declared. Its basically a copy of .t_inner, using only the margin and padding elements.
Ah, thanks. It appears I too made this mistake as my custom theme had some colors declared in this class (long before the upgrade). Corrected now!