Stones namely covered by Strokes (6)
I believe the answer is:
rubies
'stones' is the definition.
(rubies are gemstones)
'namely covered by strokes' is the wordplay.
'namely' becomes 'ie' (short for 'id est', 'that is' in Latin).
'covered by' is an insertion indicator.
'strokes' becomes 'rubs' (rub can mean to stroke or touch).
'ie' inserted within 'rubs' is 'RUBIES'.
(Other definitions for rubies that I've seen before include "Deep red gems" , "Red gemstones" , "Deep red jewels" , "The Stones in the red" .)