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