why are the leaves of my Dombeya cacuminum - Strawberry Snowball Tree yellowing??

This is quite a tender plant. Where do you live? It may be suffering from cold or low light levels. It is evergreen so it will have to drop the old leaves at some time. Are there new ones growing? A little fertiliser wouldn't hurt.

Could be magnesium deficiency. Get some epsom salts from the chemists and mix a desertspoonful to a gallon of water and feed that to them about once a month for a while.

John.