From Wiki:
The Welsh word glas is usually translated as “blue”; however, it can also refer, variously, to the color of the sea, of grass, or of silver. The word gwyrdd (a borrowing from Latin viridis) is the standard translation for “green”. In traditional Welsh (and related languages), glas could refer to certain shades of green and grey as well as blue, and llwyd could refer to various shades of grey and brown; however, modern Welsh is tending toward the 11-color Western scheme, restricting glas to blue and using gwyrdd for green, llwyd for grey and brown for brown.
In Old and Middle Irish, like in Welsh, glas was a blanket term for colors ranging from green to blue to various shades of grey (e.g. the glas of a sword, the glas of stone, etc.). In Modern Irish, it has come to mean various shades of green, with specific reference to plant hues, and grey (like the sea); other shades of green[vague] would be referred to in Modern Irish as uaine or uaithne, while liath is grey proper (like a stone).
Scottish Gaelic uses the term uaine for “green”. However, the dividing line between it and gorm is somewhat different than between the English “green” and “blue”, with uaine signifying a light green or yellow-green, and gorm extending from dark blue (what in English might be Navy blue) to include the dark green or blue-green of vegetation. Grass, for instance, is gorm, rather than uaine. In addition, liath covers a range from light blue to light grey.
I thought this was the case – hence Lôn Las Cymru (green lane of Wales) being glas rather than gwyrdd.