Ian...I don't want to dampen your creative spirit here. That is something that should be kept alive, but do you think you've created a rod for your back here?
There are so many natural colours available. Is there not one that would do the job? Is it a case of the bride having chosen her material colour and now wanting to find a flower that matches exactly. Don't know why they don't choose the flowers first as you can then get material in any shade you like!
I've had this so many times it's not funny any more. Usually try and explain that if they match the flowers to the material, it will not show up in photographs, so end up going for a contrast rather than settling for something 'similar' that may just look 'wrong'. Still not sure what your particular situation is though!