Q:

In Visual Studio, how can I change the highlight-setting(s) for @{...} bits in *.cshtml files and the like

The default highlight-settings render @{ } with a yellow background which looks like a eye-sore if the dark theme is applied in Visual Studio. 

A:

The setting which controls how @{...} bits are highlighted is called "HTML Server-Side Script" and it's located under:
Options -> Fonts and Colors -> Text Editor -> HTML Server-Side Script

