Answer: Palms are subject to infestation by scale insects so this may be what you are finding; they do occasionally pick something up while they are outdoors for the summer. They can be controlled by gently scraping them off with your fingernail and by using an insecticidal soap when they are in the soft crawling stage (they will move!) With regard to the bottom yellowing, based on your description it may be the result of overwatering during the winter when the plant slows its growth in response to the lower light level and simply needs less water as a result. You might check to make sure that the soil is slightly moist but not overly wet. You might also look carefully for any signs of mites as these can cause the foliage to stipple and appear to be yellowing. These would also be controlled with insecticidal soap according to the label instructions.
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