I know of people who use bloom fertilizers on roses & dahlias with ratios along the line of 20-150-20, but I'm a little leery of how they'll affect my plants in the long run. I've heard them say that the bloom colors were more intense in some cases & some colors were warmer, I think.

Juliet, all I "added" was cooler weather. A handy trick on my part. Ya want some?

:))

Sherry

I add blood meal to my fertilizers. The extra iron intensifies the colors, particularly the reds.

Just time, really. A well-established plant has the best color.

When I grew David Austin roses back in Washington state, I certainly noticed how pale they got in hot weather. Oddly, some Teas become pale in late fall, when light and temperatures are low. 'Mme. Antoine Mari' is white in November, quite different from her whipped cream and lilac pink tones in summer; and my normally brick-and-flame 'Général Gallieni' managed to put out a few quite lovely blooms in pale terracotta and cream before the snow and frost struck two days ago.
Melissa

i don't add anything, nothing is required. in order to promote MORE blooms, and more BIGGER blooms, the ground must be nourished: make sure to add plenty of organic mulch, for instance adding 4-6 inches of compost when heavy frost strikes, will protect the lower canes, and also feed the organisms that live in the soil, the following year. The soil then lives and breathes plants, whatever we put there (and often what we don't). The PROPER amount of bonemeal should have been worked into the soil when preparing the bed, and in the spring and summer a PROPER amount of balanced fertilizer. Micronutrients will be supplied both by the mulch breaking down, and the bloodmeal. Just check out roses growing in the wild, where only nature looks after them -- they will be plenty fragrant and colorful. Somehow society has become obsessed with "enhancement", and you see ladies all the time now putting pigments on their face - yet the natural face is actually the most expressive and prettiest and engaging. However, there actually is no "enhancement", for a rose.

One thing to work with is micro amounts of trace minerals.
A specific: I had several plants of Austin's English Elegance. They never reached the refinement of color of the photos in some of the David Austin Picture Books.
For other roses, in the same soils, the pastels developed better in late fall, but EE remained pale, even in years with more cloud cover.

Then I put wood ashes on that part of the garden, in part to suppress the 'wire grass' that was threatening to move into the garden. For the next year, EE had much improved color. That improvement happened from the very first blooms of the season. Was it the change in acidity or was it the micronutrients from the hardwoood ashes or was it both?

I don't know, but it's something you might try.

In another vein, there are articles relating to root stock choices being made to effect color of blooms. Some google book searches will lead to these. But it's darned hard to extrapolate from articles written in the past to cultivars growing in the present.

I have read each response with much interest. I find the subject fascinating. I know roses can be variable with color, but I have seen where a rose has more of an array of color subtleties in one garden and be less interesting color-wise, in another. It's not just about the color being richer, but variations in the color that can occur.

Must thank Rosecats, Sherry, The Bustopher, Hoovb, Melissa, Klinko, and Ann for the inspiration of using wood ashes to affect soil ph, or add trace minerals. Very interesting indeed!

Juliet