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