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