One vertex per element, one color per generator, with an edge from x to x·s.
(1,2,5,3)(4,7,8,6)(9,10,15,16)(11,17,12,21)(13,22,23,18)(14,19,24,20)(26,30)(28,35)(31,36)(34,39)(2,3)(6,7)(10,16)(13,23)(17,21)(19,20)(27,33)(31,36)(34,39)(38,40) involution — undirected(1,3,5,2)(4,7,8,6)(9,11,15,12)(10,17,16,21)(13,20,23,19)(14,18,24,22)(25,26)(27,31)(28,32)(29,30)(33,36)(34,38)(35,37)(39,40)(1,4,5,8)(2,6,3,7)(9,12,15,11)(10,17,16,21)(13,19,23,20)(14,18,24,22)(25,27)(26,31)(28,34)(29,33)(30,36)(32,38)(35,39)(37,40)(9,13)(10,18)(11,20)(12,19)(14,21)(15,23)(16,22)(17,24)(25,28,29,35)(26,32,30,37)(27,34,33,39)(31,38,36,40)(9,14,15,24)(10,19,16,20)(11,18,12,22)(13,21,23,17)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.