The leaves of Chinoides are naturally a pale olive green, not the deep forest green of some varieties. Lower leaves yellow in all rhododerons as they reach the point where they are about to be shed - completely natural process. The yellowing of all the leaves can be the result of lack of water - if you've had a dry summer, this is the most likely cause, especially if the root ball was not loosened and thoroughly moistened at the time of planting.

Don't add nitrogen now. It will stimulate late vegetative growth which will likely winter kill. Sulfur is sometimes used as a soil acidifier, but there are better ways to accomplish this. In fact, don't add sulfur or anything else unless a soil test indicates a need.