It's more a case of what exactly do you call the shade of blue. The CR appears to have had a fairly dark ultramarine blue to begin with, which was later changed to a royal blue. Yes, the lighter blue was as a result of the painters mixing in white. They were paid per locomotive and as the blue didn't cover well, and so needed several coats, mixing in the white required fewer coats.
I have to confess that many CR locos looked rather handsome in red in later years, but then they were handsome locos anyway. However, that period is far too modern for my taste!
Jim