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