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