change the default test coverage colors
change the default test coverage colors

After some consultation with my class this quarter,
it seems clear that the previous defaults and nearby
variations are completely hopeless for colorblind people
(there are at least 3 in this class). So go with the
defaults used in the HtDP languages, which have been
vetted by saidsame 3 people.

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket