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