Be more obvious between environments

[gak]

A simple fix would be allowing a filter to apply a style class to particular values shown in the nav bar.

A more difficult one I've tried before is to change the colour of the whole top bar for an important filter, e.g. viewing production logs. This was complex because of the multiple styles using the same colour explicitly in the nav dropdowns, etc.

I think go with the first, and if the second is too complicated, create a separate issue.