On my Mandeville plant, I have some yellow leaves with spots on them.
I Have Some Yellow Leaves With Spots on Them
Certified GKH Gardening Expert
Check the leaves and plant for any signs of bugs or insects.
If found you can treat with insecticidal soap or Neem Oil.
However the yellowing leaves could be from watering issues, to much or to little.
Environmental issues can be a cause as well as natural aging of the plant.
Here are two great links to help you pinpoint the issue.