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