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