Stray that's pale turning red (6)
I believe the answer is:
wander
'stray' is the definition.
(I know that stray can be written as wander)
'pale turning red' is the wordplay.
'pale' becomes 'wan' (wan can mean pale or grey).
'turning' says the letters should be written backwards.
'red' in reverse letter order is 'der'.
'wan'+'der'='WANDER'
'that's' acts as a link.
(Other definitions for wander that I've seen before include "Go to and fro" , "endless travel" , "Move about aimlessly" , "Roam around aimlessly" , "Stroll" .)