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