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