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