Not sure if this is gonna help, because I don't know if it's an actual game fact or it was just a fortunate coincidence for me, but... Listen, please.
I too had such a frustrating time until I bred my first blue rose! But at some point, I got eight of the second-bred red roses and decided to try out some rumor I had read on internet. Since it was long ago that I had a perfect town score continously, a few Jacob's Ladder had appeared on my cliffs. So, I made a breeding square with those eight red roses and put a Jacob in the middle. Watered them every day with the golden can. Only 4 days later, a new blue had sprouted! While the first one had taken me almost three months.
So, the rumor was that Jacob's Ladder helped breeding. I repeat, not sure if that's what truly happened or I was just lucky, but if you have the perfect town score already and a Jacob or two, it's worth trying.