I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
Very strange. Yellow older leaves are usually a sign of too much or too little water, or possibly some root or lower stem rot diseases (often brought on by soggy conditions). The dark green to blue spots do not fit any specific problem with those hibiscus plants and are probably not due to any problem but rather just part of the leaf loss process.
Thanks for the question. Please stop in again soon!
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