Small mark left by wound? It's red (7)
I believe the answer is:
scarlet
'red' is the definition.
(I know that red can be written as scarlet)
'small mark left by wound? it's' is the wordplay.
'small mark left' becomes 'le' (I can't explain this - if you can you should believe this answer much more).
'by' says to put letters next to each other.
'wound?' becomes 'scar' (I've seen this before).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'le' put after 'scar' is 'scarle'.
'scarle'+'t'='SCARLET'
Can you help me to learn more?
(Other definitions for scarlet that I've seen before include "immoral" , "Murderer" , "Crimson" , "Bright red of clarets" , "bloody?" .)