It turned green if it was not planted in peat which is needed to keep it green you could try digging as much of the soil around and as deep out and filling the space with peat but if it is an established tree you might not get any change in colour.

Erm, that answer isn't accurate, Yoyo, I' afraid.

First Eddie, next time you post something, hit the space bar between words, its easier to read than one long string of letters. Second, have the conditions around your Acer changed? Many only colour up red or whatever if they have some sun exposure, so if there's a tree or building or something else now shading the Acer totally when it had some sun previously, that would explain it.

Otherwise, post a photograph please.

Thats happening to my Acer drumondii, the side in the shade is green instead of variegated,not reversion I think, just not enough light

Also although some acers are very red at the start of the growing season by now the underside of the leaf is often green and the top a sort of rusty red rather than the bright red.

Hitting the space bar and adding punctuation takes no time at all...

Oh I dunno, Rosierose, if you're not used to a keyboard, electronic or otherwise, it does take longer, Ive seen my ancient mum try to type...

And predictive text is a pain!

Too right, Pamg - I never understood why, if you tried to type Mum, it offered you 'nun', I mean how often are you ever likely to type the word 'nun' for heaven's sake. That particular annoying feature was very firmly switched off...