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