"I do not have grey hair yet."
Translation:Chan eil falt liath orm fhathast.
Celtic colours do not match English ones. Glas is 'bluish-greenish-greyish' and liath is 'lightish-greyish'. Glas has actually become 'blue' in Welsh and 'green' in Irish.
But more importantly, certain words are used for certain things in any language and liath is simply the correct word for grey hair in Gaelic.
As I said, Gaelic colours do not match up with English ones. Gorm and blue have overlapping ranges so one is often the correct translation, but there are lots of blue things that are nowhere near gorm, such as the light blue sky we often get in Scotland, as opposed to the dark blue sky you sometimes see in the Mediterranean.
It is worth pointing out a pedagogical difference between the Celtic languages. Whilst they teach that glas means blue in Welsh and green in Irish, they are always careful to avoid this in Gaelic. They always explain from the outset that the colours do not match up. Similarly they teach that the Irish word gorm = blue, but they avoid doing this in Gaelic, having learnt from the other languages which have been taught far longer than Gaelic.
For this reason, statements like 'gorm means blue' should be avoided for Gaelic, even if they are OK for Irish.