It's in ~amd64 for 4 months already and works fine. No bug reports on the project's GitHub issue tracker either. Should probably be ALLARCHES as it's just a perl/shell script.
arm done
x86 stable
sparc stable
ppc64 stable
hppa stable
Looking good on ppc. # cat colordiff-740460.report USE tests started on Sa 12. Sep 13:24:11 CEST 2020 FEATURES=' test' USE='' succeeded for =app-misc/colordiff-1.0.19 USE='' succeeded for =app-misc/colordiff-1.0.19 revdep tests started on Sa 12. Sep 13:27:59 CEST 2020 FEATURES=' test' USE='colordiff' succeeded for app-portage/conf-update
ppc stable thanks to ernsteiswuerfel!
amd64 stable. Closing.