An arresting shade? (3)
I believe the answer is:
red
'shade?' is the definition.
(red is a colour or shade)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for red that I've seen before include "Colour of communism" , "Colour for danger" , "- - poker: Kniphofia" , "Colour of blood" , "Flushed" .)