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