Absurd to change leader -- that's plain to see (7)
I believe the answer is:
visible
'plain to see' is the definition.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for visible that I've seen before include "Perceptible by the eye" , "In view" , "Able to be seen" , "In sight" , "Showing up" .)