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