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