Appeared and endlessly vented, having spent too long on the sunbed (7)
I believe the answer is:
entered
'spent too long on the sunbed' is the definition.
I can't tell whether this defines the answer.
'appeared and endlessly vented' is the wordplay.
'appeared' becomes 'red' (I am not sure about this - if you are sure you should believe this answer much more).
'and' is a charade indicator (letters next to each other).
'endlessly' indicates the central letters (the ends of the words are removed).
The central letters of 'vented' are 'ente'.
'red' after 'ente' is 'ENTERED'.
'having' acts as a link.
Can you help me to learn more?
(Other definitions for entered that I've seen before include "Logged; arrived" , "Ten deer (anag) - went in" , "moved in" , "Came in; recorded" , "Enrolled or went in" .)