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