  We present a edge-coloured analogue of the duality theorem for transitive
tournaments and directed paths. Given a edge-coloured path $P$ whose edges
alternate blue and red, we construct a edge-coloured graph $D$ so that for any
edge-coloured graph $G$ $$ P \to G \Leftrightarrow G \not\to D. $$ The duals
are simple to construct, in particular $|V(D)|=|V(P)|-1$.
