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