Rare green gems (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
emeralds
(Other definitions for emeralds that I've seen before include "Green stones from strangely red males" , "Precious stones for odd red males" , "They're preciously green on the Isle" , "Mere lads (anag.)" , "Colours" .)