Question
why would the leaves on the rose plants be turning a dull green, no shine to them anymore.

Answer
Not being able to look at the leaves I will have to take a guess. When a rose has a shine on the leaves, they can have a shine because they are new leaves. But when they get older they then turn to a dull green. However when a rose is under stress and is starting to die from lack of water or anything else, the leaves will go a dull, dusty green. Check your rose carefully and see if you can find a lump on a cane at the base, dry soil farther down even if the soil looks damp on top and last, scratch the canes near the top to see if they are green under the outside bark. If they are a brown colour then the rose is dying. If they are green it may just be how that rose grows.