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