It is not known for certain but a virus infection is believed to be the cause of yellow marks or mottling on the foliage of camellias. Not all the leaves are affected and the plant will still produce good flowers, some variegated.

Control:
Only a few leaves are usually affected with the spotting and these can be cut off and destroyed.

A diseased plant should not be used for grafting and although the problem is not very serious in the home garden, if you grow a lot of camellias you should consider removing an infected plant to prevent any possibility of transmission to other, healthy specimens.