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