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