improve legends in histograms

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

00:09:49

83.0%
passed build_linux_36 #135460
docker

00:22:00

83.0%
passed build_macosx_27 #135461
macosx

00:23:09

83.0%
passed build_macosx_36 #135462
macosx

00:22:33

83.0%