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