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