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)(19,32)(23,38)(24,34)(27,33)(29,35)(30,37)(31,36)(39,40) involution — undirected(2,5)(6,8)(9,11,15,25)(10,17,21,18)(12,14,24,16)(13,23,31,39)(19,35,37,33)(20,34,22,26)(27,30,29,32)(28,40,36,38)(1,3,4,7)(2,6,5,8)(9,12,16,11,15,24,14,25)(10,18,22,26,21,17,20,34)(13,29,32,39,31,27,30,23)(19,33,28,40,37,35,36,38)(9,13,14,30,15,31,16,32)(10,19,20,36,21,37,22,28)(11,23,12,27,25,39,24,29)(17,33,26,38,18,35,34,40)(2,5)(6,8)(9,14,15,16)(10,20,21,22)(11,24,25,12)(13,30,31,32)(17,34,18,26)(19,36,37,28)(23,29,39,27)(33,40,35,38)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.