One vertex per element, one color per generator, with an edge from x to x·s.
(2,5)(6,8)(9,10)(11,12)(13,17)(14,15)(16,20)(18,19)(21,22)(23,24)(25,26,31,32)(27,29,30,33)(28,34,38,39)(35,37,36,40)(1,2)(3,6)(4,5)(7,8)(26,32)(27,30)(34,39)(35,36) involution — undirected(1,3,4,7)(2,6,5,8)(10,15)(11,16)(17,22)(18,23)(25,27,31,30)(26,33,32,29)(28,36,38,35)(34,37,39,40)(9,11,14,16)(10,12,15,20)(13,18,21,23)(17,19,22,24)(25,28,31,38)(26,34,32,39)(27,35,30,36)(29,37,33,40)(9,12)(10,16)(11,15)(13,19)(14,20)(17,23)(18,22)(21,24)(25,29,31,33)(26,27,32,30)(28,37,38,40)(34,35,39,36)(9,13,14,21)(10,17,15,22)(11,18,16,23)(12,19,20,24)(25,30,31,27)(26,33,32,29)(28,36,38,35)(34,40,39,37)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.