So I've come back to using ConTeXt after a year away from it (publishers
preferring LaTeX, y'know), and in revising some student notes I'm getting
errors which seem new.

For a collection of overheads, I've set up

\setupbodyfontenvironment[default][em={\slanted\color[red]}]

However, when I run context on my files, a command such as {\em elephant}
produces:

l.3 The {\em
           elephant} is a large gray animal
? h
The control sequence marked <to be read again> should
not appear between \csname and \endcsname.

What's going on here, and how do I fix it?

Thanks,
Alasdair