In excursion round Rhode Island, pass flag (9)
I believe the answer is:
tricolour
'flag' is the definition.
(I know that tricolour is a type of flag)
'in excursion round rhode island pass' is the wordplay.
'in' indicates putting letters inside.
'excursion' becomes 'tour' (I've seen this before).
'round' is an insertion indicator.
'rhode island' becomes 'RI' (US postal abbreviation).
'pass' becomes 'col' (col is a term for a mountain pass).
'tour' going around 'ri' is 'triour'.
'triour' placed around 'col' is 'TRICOLOUR'.
(Other definitions for tricolour that I've seen before include "French national flag" , "Having or involving three colours" , "Standard of French perhaps" .)