Teddahlia that deep purple Dahlia color is spectacular!
How to come up with one color for the Dahlia? Humm, that might take some trial and error. I really like your idea of blurring the image. I actually did blur images using an open source image processing library and Python in 2008. We turned the images into color histograms, and then tried to identify the blurred image (document) based on the histogram similarities.
As with many software solutions, one solution may not fit every "use case". Bi-color Dahlias and peony Dahlia with prominent yellow centers come to mind as special cases. If you think it's worthwhile, should we start a new thread and talk about what the software "use cases" would be? More than one person could answer the question "What would you want the Dahlia color app to do?" "What would you use it for?", etc. A simple solution is always better.