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