I am hoping you can answer a question for me in regards to my Harlequin Maple. I planted one in my Kitchener garden and it was beautiful and had the very distinctive colouring. We moved to Manitoulin Island in 2006 ..zone 5A and I loved the tree so much, we bought another and planted here. The tree is growing well but the colour is not the same. Rather than being green with the distinctive lighter edge, it is green with just a lighter shade of green along the edge. Its it due to the acidity or lack of in my soil?
The variegation on your Harlequin Norway Maple, or Acer platanoides ‘Drummondii’, could be decreased by the amount of light it is receiving. Is your tree shaded by other more mature trees? Heavy shade will affect the brightness of the leaf colour. This tree should ideally be grown in full sunlight to bring out the best contrast in leaf variegation. It is not particular as to soil types or pH levels, but does prefer to grow in average to moist conditions and should not be allowed to dry out.
It is worth mentioning that this cultivar is known to revert back to its original green colour. Although this might not be the exact issue you are dealing with, if you do notice solid green leaved branches appearing it is recommended to remove the green leaved limbs which can grow more aggressively than the variegated branches and ultimately take over the tree. An interesting article on this phenomenon can be found at https://www.leevalley.com/en/newsletters/Gardening/1293/Article2.htm should you want to learn more.