Ans: A graph colouring is a method of allocating colours to the vertices of a graph so that no two adjacent vertices get the same colour.Few graph colouring issues are:Vertices Colouring - It is a method of colouring the vertices of a graph in such a way so that no two adjacent vertices share a similar colour.Edge Colouring - It is a method of allocating the colours to edges of a graph in such a way so that no two adjacent edges share a similar colour.Face Colouring - It is a method of allocating colours to each face or region of a graph so that no two adjacent faces of a graph share similar colours.