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