Tony,
My (far from extensive) research has revealed no definitive information re. original engine colours for the B2.
As you say many are black but there also seem to be about as many in green among the many pictures on the interweb.
I can only suggest you contact L’Aventure (ex Conservatoire) and ask them.
email: conservatoire@citroen.com tel: + 33 1 56 50 80 20
B….
Bernie