During trip, Rhode Island pass makes one flag (9)
I believe the answer is:
tricolour
'one flag' is the definition.
(tricolour is a kind of flag)
'during trip rhode island pass' is the wordplay.
'during' indicates putting letters inside.
'trip' becomes 'tour' (I've seen this before).
'rhode island' becomes 'ri' (US postal abbreviation).
'pass' becomes 'col' (col is a term for a mountain pass).
'ri'+'col'='ricol'
'tour' enclosing 'ricol' is 'TRICOLOUR'.
'makes' acts as a link.
(Other definitions for tricolour that I've seen before include "French national flag" , "Standard of French perhaps" , "Having or involving three colours" .)