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