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