Under most natural circumstances, it would be unlikely that koalas would seriously affect eucalyptus trees. Their territories and social structures would help to ensure that individual trees or parts of their habitat wre not heavily browsed or harmed. The koalas that remain in such areas are generally unable to access other areas of habitat due to massive clearing and are likely to eventually become malnourished, sick and die. We work hard to identify and protect important habitats and to promote restoration where required. Ash-grey is one of the variations in colour that koalas have.
Some koalas look sort of chocolatey brown.
In the northern parts of Australia where the climate is hotter, koala fur is lighter in colour - mostly ash grey. Yes, 'no drink' is the meaning generally attributed to the word 'koala', although in reality, there were hundreds of different aboriginal languages, so they called koalas a range of different words including cullewine, boribee, koolewong, colo, colah, koolah, karbor, goribun. I've heard that in some dialects the word used to describe koalas meant 'grumpy fellow' or 'old man'. Koalas occasionally drink water but they do get most of the water they need from the eucalyptus leaves. Yes, the main threat to koalas is that we humans are clearing their habitat.