Orthogonal Vector Coloring
A vector coloring of a graph is an assignment of a vector to each vertex where the presence or absence of an edge between two vertices dictates the value of the inner product of the corresponding vectors. In this paper, we obtain results on orthogonal vector coloring, where adjacent vertices must be assigned orthogonal vectors. We introduce two vector analogues of list coloring along with their chromatic numbers and characterize all graphs that have (vector) chromatic number two in each case.
Haynes, G., Park, C., Schaeffer, A., Webster, J. & Mitchell, L. (2010). Orthogonal vector coloring. The Electronic Journal of Combinatronics, 17(1), R55, 18. https://doi.org/10.37236/327.