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