In Irish, 'glas' means 'green'. The notes here say something woefully brief about Celtic languages traditionally describing green as blue. Can anyone elaborate? Green is NOT blue, as far as I'm concerned!
glas in Welsh does mean blue, and it is normally translated as that.
It is also sometimes used for shades of bluey-green and for the idea of 'fresh green', as in newly grown grass and plants. People who are inexperienced in things may also be described as glas or termed gleision, similar to the English 'green', 'greenhorns', 'freshers'.
The section notes have now been expanded a little.