Three-coloured

Question

I’ve only ever seen the adjective tricoloured ie. similar to French, in English

Maarten Kamp · Accepted Answer

Anita, 
a number of resources, including wordreference as below, indicate tricoloured and three-coloured as synonyms, although in reference to the French flag specifically or to other ‘ three-coloured’ flags in general, I would also tend to use ‘le Tricolore’, or ‘ tricoloured ‘ flags respectively. 
https://www.wordreference.com/fren/tricolore
 https://www.institutdefrancais.com/french-flag-colors-meaning/

Céline Pickard · Answer

Bonjour Anita,
Maarten's correct! However, I have never heard French natives use the term "le Tricolore" when referring to the French flag. But then, it might just be me and my own group of friends/family.
Here's a site you might useful about the French flag and its origins:
Le drapeau français - Élysée
I hope this is helpful.
Bonne journée !