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