When I hear \"yellowed showing veins of green\" I think lack of iron. There is also this same yellow foliage if you water too much or the plants are lacking in any nutrient. First, feel the soil and if it is damp do not water until the top few inches are dry. Then apply a slow release plant food like Osmocote and see if the foliage greens up in a few weeks. If nothing happens, try adding an iron chelate product following the instructions on the package. Lack of iron is mostly just for acid loving plants like rhododendrons, camellias and gardenias. Too much water is more common for potted plants especially during cool, rainy weather. If you would like to send a photo that would help in solving this mystery. Keep growing, Marianne Binetti