Surrealist painter touring India, initially watching Hindu festival (6)
I believe the answer is:
diwali
'hindu festival' is the definition.
(Hindu festival of light)
'surrealist painter touring india initially watching' is the wordplay.
'surrealist painter' becomes 'dali' (I've seen this before).
'touring' means one lot of letters goes inside another (touring can mean going round).
'india' becomes 'i' (phonetic alphabet: alpha, bravo, charlie etc.).
'initially' suggests taking the first letters.
The initial letter of 'watching' is 'w'.
'i'+'w'='iw'
'dali' placed around 'iw' is 'DIWALI'.
(Other definitions for diwali that I've seen before include "Hindu festival; I'd wail (anag.)" , "Festival in honour of Lakshmi" , "Light festival" , "Indian festival" , "religious festival" .)