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