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