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