erp5_web_renderjs_ui: Set label color or required field to black

to make the difference with other fields more visible
5 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:03:37

passed ERP5.PerformanceTest-Master

00:32:21

passed ERP5.UnitTest-Master

01:51:31

passed SlapOS.Eggs.UnitTest-Master.Python2

00:14:58

passed SlapOS.Eggs.UnitTest-Master.Python3

00:14:49