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