If it is largish yellow areas - sounds as if it needs a good rose feed? Buy one which contains Epsom salts? Black spots are disease and again you need a rose black spot spray and remove any debri around the roots. If you had a pic we could perhaps stop guessing?

Certainly sounds like rose black spot to me. Pick off all the affected leaves and dispose of them (do not compost them). Also pick up any leaves lying on the floor around your rose(s) to help stop it spreading. If you catch it early enough you may get away without needing to spray. But, as Drc726 says, a pic would be useful.

Agree with the others, a photo is essential really.l

I think I found the culprit - there was a sandy looking very small beetle/bug on the leaves who was sort of draining the leaf from the underside. I will probably spray once the sun has gone in and hopefully that will deal with it. I will post a photo too when I get a chance - as the effect is quite beautiful really! Its definitely not blackspot though.