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