I doubt that the Bayer had any effect on the color. Most probably it's due to a difference in the weather. Temperatures and amount of sunlight can have a big effect on rose colors. If they're blooming a month earlier than last year then the sun is a month lower in the sky and they aren't getting as much sunlight.

Thanks! I did notice several rose bushes close to where I live have also bloomed early this year, it did not seem to bother them at all. They all look quite brilliant.

I read somewhere that too much growth in leaves and stems (due to too much nitrogen if I recall correctly) can come at the expense of the flowers. I am not sure whether the size or the color of the flowers can be affected this way...

Yes, look up the temperatures leading up to the bloom--lots of cool weather before a bud blooms will result in the best colors and largest bloom size. Hot weather will even turn normally double blooms to singles. No, roses need plenty of nitrogen--the best flowers come off of big healthy plants--which is why exhibitors will often have programs that maximize the amount of nitrogen fed to the plant--sometimes feeding the plant every week.