Garden Q&A: The leaves on my red camellia are yellow. How can I make it healthier?

Camellia 'Debbie ' Kells Bay House & Gardens, Co Kerry. Picture Dan Linehan
I am looking for a Camellia Debbie but cannot source in my garden centres in East Cork. Can you advise me of any variety which may be a similar colour, please? Also, I have a red camellia in my front garden which is on a slant. It has plenty of buds but the leaves are yellow. Can you advise me as to what I can do to make the shrub look healthier, please? I have rhododendrons and camellias already in my garden so I know my soil is ok.