On the existence and non-existence of improper homomorphisms of oriented and $2$-edge-coloured graphs to reflexive targets

We consider non-trivial homomorphisms to reflexive oriented graphs in which\nsome pair of adjacent vertices have the same image. Using a notion of convexity\nfor oriented graphs, we study those oriented graphs that do not admit such\nhomomorphisms. We fully classify those oriented graphs with tree-width $2$ that\ndo not admit such homomorphisms and show that it is NP-complete to decide if a\ngraph admits an orientation that does not admit such homomorphisms. We prove\nanalogous results for $2$-edge-coloured graphs. We apply our results on\noriented graphs to provide a new tool in the study of chromatic number of\norientations of planar graphs -- a long-standing open problem.