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