I have a sago in a pot. I usually have it in the sun. I noticed it was turning yellow. I live in central Texas (HOT) So I moved it so it would be part sun--early am-- and then shade in afternoon. That did the trick. I didn't know the full hot sun would be a problem and had put in 2 more sagos in the front yard, full sun, nearly lost them. dug them up and put them in pots and now I'm trying to nurse them back to health. I just did this a few days ago and already see a difference in their color. Odd, too, because just around the corner from us is a beautiful yard with very mature--bloomed this year--sagos about 5' tall, full sun. But maybe the roots are very deep and can cope with the heat. So you might think about the sun as a problem but they yellow because of too much water, too, so think about how much your are watering, that might be the problem. Side note: I found that they really like a shot of miracle grow from time to time. HTH