General & Others Black CoA is too ugly

The Haki System by itself is a great idea. My only problem is the inconsistency of coating black or not, when Haki is been used. For example:
  • We know that Luffy used Haki on the Pacifista after the timeskip, but without black coating.
  • Till Wano we didnt see any coating of Sanji (only clearly visible trough Anime).
  • The worst part was the black shading of Devil-Robin, where its still discussed whether she used Haki or not.
  • From the Flying 5 only two (dunno if also Page One) showed they black coating
Its just confusing and to much time is being wasted on asking "Does he or she has Haki?; did they use haki?; blablabla".