Now's the end of September, but willows didn't turn yellow. However, from houses and backyards appeared yellow and purple-red trees. Willow is a type of tree, however unless you want to talk about willows specifically I recommend changing the tree for this story as most people don't know what willows are. Something like maple, oak, and so on would be better choice. Also when you described the color of the tree, you could have changed it up slightly to make it sound more mature, but you did good.

Ok, Thank you!

Correction: inversion, not conversation. The sentence element is "However from houses, from backyards " -- without this element before the verb, you couldn't do the inversion. Usually, negation elements are used in such an inversion situation, for example: "Never had John seen such a sight."

Thank you, Phil! But what the sentence element you talking about? Preposition? or "of trees"?

As far is the use of conversion, it's correct, although optional. Note that there is a sentence element before the verb, and also that the verb is intransitive.