One vertex per element, one color per generator, with an edge from x to x·s.
(2,4)(6,8)(26,31)(27,33)(32,39)(34,35) involution — undirected(3,7)(6,8)(9,10,14,11)(12,15,20,17)(13,16,21,18)(19,22,24,23)(25,26,30,31)(27,29,33,38)(28,32,37,39)(34,36,35,40)(1,2,5,4)(3,6,7,8)(10,11)(13,21)(15,17)(19,24)(27,33)(29,38)(34,35)(36,40)(9,11,14,10)(12,15,20,17)(13,18,21,16)(19,22,24,23)(25,27,30,33)(26,29,31,38)(28,35,37,34)(32,40,39,36)(1,3,5,7)(2,6,4,8)(9,12,14,20)(10,15,11,17)(13,19,21,24)(16,22,18,23)(25,28)(26,32)(27,34)(29,36)(30,37)(31,39)(33,35)(38,40)(1,4,5,2)(3,8,7,6)(9,13)(10,16)(11,18)(12,19)(14,21)(15,22)(17,23)(20,24)(25,29)(26,33)(27,31)(28,36)(30,38)(32,35)(34,39)(37,40)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.