Salad ingredient princess spots outside (6)
I believe the answer is:
radish
'salad ingredient' is the definition.
(radishes are often used in salads)
'princess spots outside' is the wordplay.
'princess' becomes 'di' (Princess Diana).
'spots' becomes 'rash' (I've seen this before).
'outside' means one lot of letters goes inside another.
'di' inserted into 'rash' is 'RADISH'.
(Other definitions for radish that I've seen before include "Red cold salad ingredient" , "Root vegetable used in salads" , "Pungent red salad root" , "Root eaten raw in salads" , "Hottish salad plant" .)