Here are three photos from the same bush, under the same full sun lighting conditions. The first photo was taken Sept 2010, the second photo is dated Sept 1, 2013, and the last one was take Sept 29, 2014. In these last years, the yellow is mostly gone.
Parentage: 16D07 Jelinek was crossed from 22C03 Jelinek X Judy Garland, Harkness.
22C03 Jelinek was crossed from Tournament of Roses X Lady Jane Grey, Harkness
16D07’s grandparent, Judy Garland, has Circus crossed into it twice, according to Modern Roses XII. (Circus is a rose that changes color.)
On other crosses where Circus was not involved, in a lot of cases I have noticed that the first bloom from seed is brighter and seems superior to the subsequent blooms as the plant bushes out.
Photo tropic blooms change dramatically with heat and light intensities. My bet would be the air and light temps and intensities were probably greater for the darker, less yellow photos than for the earlier, more yellow ones. How has your climate varied each year from 2010 through 2014? Without researching it, simply from the appearance of the flowers, my bet would be each year has been warmer than the preceding one.
I have quite a few phototropic roses and find that the amount of humidity and the night time temps are quite influential with their coloration swings, more so than what time of the yr it is. I really think that the springtime colors are most constant, but I am pretty sure that a springtime heat spell would still effect coloration. Nice coloration on the latest photos.
Bloom quality should improve over time all other things being equal and disease not being a problem (especially gall and nematodes).
I doubt your environment is responsible given where you are. My guess is nutrition is a factor, particularly phosphate. Soluble fertilizers don’t always cut it in that regard even when they have high phosphate. Try breaking up some egg shells around the base of the plant, the more the better. If you don’t already do so try incorporating rock phosphate into the soil when you plant out your seedlings.
