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)(11,17)(12,15)(13,16)(14,19)(18,23)(20,22)(21,24)(27,34)(31,39)(35,38)(36,40) involution — undirected(9,11,13,19)(10,14,16,17)(12,18,20,24)(15,21,22,23)(25,26,30,32)(27,35,34,38)(28,29,37,33)(31,40,39,36)(1,3,5,4)(2,6,7,8)(9,12,13,20)(10,15,16,22)(11,18,19,24)(14,21,17,23)(25,27,28,36,30,34,37,40)(26,31,33,35,32,39,29,38)(10,16)(14,17)(15,22)(21,23)(25,28,30,37)(26,29,32,33)(27,36,34,40)(31,38,39,35)(1,4,5,3)(2,6,7,8)(11,19)(14,17)(18,24)(21,23)(25,29,28,26,30,33,37,32)(27,35,36,39,34,38,40,31)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.