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