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