Yes, I quite noticed that too. It is because the Active Font colour seems to be grey too. I changed my Active Font colour to dark Green using theme customizer and that way it seemed to be visible. @AlMehdi: I would like to request changing the Active Font colour to something more visible. Grey makes all the emails look like they are all read... Just a small difference in colour between Active and primary makin it quite difficult.So May I suggest a Dark Green Shade. It goes perfectly with the outline too. Try #619200 for the Active Font.