Chart-topper penned by our group is unblemished (5)
I believe the answer is:
white
'unblemished' is the definition.
(white can mean unstained)
'chart-topper penned by our group' is the wordplay.
'chart-topper' becomes 'hit' (as in a hit record).
'penned by' indicates putting letters inside.
'our group' becomes 'we' (we or us).
'hit' put inside 'we' is 'WHITE'.
'is' is the link.
(Other definitions for white that I've seen before include "11's domicile" , "Having pink skin" , "Very pale; morally pure" , "Neutral colour" , "and 9: What Bing Crosby dreamed about" .)