Nasties are usually a plant and forget them plant; they don't require much care. Do you always plant them in the same place? Maybe it is too wet.

Yellow leaves on any plant is usually a sign they are too wet or too dry or lack of fertilizer. Nasties don't like much fertilizer, so I'm thinking it could be one of the other 2, unless the leaves also have spots.

If that's the case then you have a fungal disease called leaf spot. Leaf spot is treated with fungicide after picking off all the diseased leaves and cleaning up any debris on the ground. Don't water the foliage only the ground. You may have to use the fungicide often to get rid of it

I have grown the Alaska Mix for 2 years now and have Empress of India this year also. I think that as the leaves age they turn yellow. I only get one or two on a plant though. I simply trim them off. But if your whole plant has yellow leaves then you may have a problem, perhaps with too much water.