improve legends in histograms

4 jobs for hist in 54 minutes and 58 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Build
passed #135459
docker
build_linux_27

00:09:49

83.0%
passed #135460
docker
build_linux_36

00:22:00

83.0%
passed #135461
macosx
build_macosx_27

00:23:09

83.0%
passed #135462
macosx
build_macosx_36

00:22:33

83.0%