The export dispatcher's active keys are highlighted using the
'org-warning' face.  That face is applied in various contexts, including
the agenda.

Users who have difficulty reading the active keys of the export
dispatcher are therefore forced to modify 'org-warning' throughout their
setup, even though their problem is present only while viewing the
dispatch UI (because highlighted keys are one or a few characters long).

The attached patch is an attempt to address this issue by creating a new
face that is specifically designed for the dispatch UI.

For the background+foreground combinations, the selected values conform
with the highest accessibility standard for colour contrast (WCAG AAA,
else a minimum contrast ratio of 7:1).  I limited my options to what
'M-x list-colors-display' provides.

Best regards,
Protesilaos

-- 
Protesilaos Stavrou
protesilaos.com