Potted trees yellowing?

[catscratch]

Rootmaker 18's have started to yellow. It's time to either transplant into bigger pots or final location. I'm thinking nitrogen but don't want to stimulate new growth right before winter. The bottom pic is a normal colored tree in a larger pot.
What's my next move?

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[dogdoc]

I think your next move is what you suggested. Larger pots to over winter or plant in their forever home.