The phrase "becomes grey" is correct and usable in written English.
You can use it to describe the color change of something. For example: "The sky becomes grey as the storm approaches."
As soon as you live in the place, it becomes grey and miserable – as do the people.
As spraint ages it becomes grey and crumbly, eventually disappearing, until only the prey remains are left.
First the status bar becomes grey and flickers and the touchscreen becomes unresponsive, with users unable to control or use the smartphones without the touchscreen working.
Later, thanks to the great Paule Constable's lighting, that shingle becomes grey, and risen around Stevenson's neck like a surgical collar.
Integrating young immigrants into the workforce is the "biggest challenge by far".Much therefore depends on how gracefully Germany becomes greyer and browner.
Lava flows appear black; as they age, they fade and become grey.
Mortal Kombat In 1992 Nintendo forced the game's creators to replace its notoriously gratuitous gore with more sanitised scenes; animations of red "blood" became grey "sweat".
As people continue to get older, eventually the hair will become grey all over – something that I hope doesn't happen to me for an extremely long time.
His B of the Bang sculpture in Manchester was dismantled after it started shedding metal, and his Blue Carpet in Newcastle was late and over budget and in the space of a few years became grey and shabby.
Video footage of the former Iraqi president undergoing a medical examination after he had been captured showed a dishevelled figure with unkempt dark hair and a thick beard that had become grey.
The water shined in the dying light, and the distant sky had transformed into a canvas of purples and reds, soon to become grey, then black.
