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