"I have a gray sweater on."
Translation:Tha geansaidh glas orm.
I’d say it’s a common misconception (or at least huge simplification) that in Irish “glas means green”.
Glas means less saturated natural green, and also gray, and also less saturated blue in Irish; while uaine is more vivid green (and green only). Eg. féar glas is green grass but Irish flag has the colour uaine, and capall glas is a gray horse (and definitely not a green one), caora ghlas a grey sheep, flainín glas grey flannel, spéir ghlas grey sky, lúireach ghlas bright corslet etc. See examples at Foclóir Gaeilge-Béarla.
And this image showing colours in Irish (glas defined as light blues, greys, greens of the sea and grass), link:
(edited) Sure, now in Scottish Gaelic glas rather means gray while in Irish the same glas more often means green (while Gaelic would rather use uaine or even gorm, eg. green grass in Irish being the aforementioned féar glas in Irish but feur gorm in Gaelic, but still ubhal glas for green apple) but I’d tend to think it’s an English influence and newer tendency to force Gaelic vocabulary into the typical western scheme of colours with green, blue, and grey clearly separated.