I had three maples in the garden in my last home and they had lovely (non-green) coloured leaves on them there. I have now replanted them in my new home and all I get now is just green leaves.
Why don't they have the colour they used to have?
There is an article on the net describing the causes of similar behaving of maple color.
It basically says that japanese maples may become more 'green' if:
Seattle Japanese Garden also offers a very good article 'Gardeners' Talk: Autumn Colors and Japanese Maples'on maple autumn colors. Key point:
The brilliance of color is thought to be most affected by temperature, light, and soil moisture, not just fall but all through the growing season. It is suggested that an ideal combination would be a wet warm spring, a summer that is not too dry, and an autumn filled with dry days and cool nights.