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)(11,19,20,37)(12,23,27,38)(13,28,25,18)(15,30,31,21)(16,33,35,26)(22,39,29,34)(24,36,40,32)(2,5)(3,8)(6,7)(15,31)(19,37)(32,36)(34,39) involution — undirected(1,2)(3,6)(4,7)(5,8)(9,11,14,20)(10,15,17,31)(12,24,27,40)(13,29,25,22)(16,34,35,39)(18,36,28,32)(19,38,37,23)(21,33,30,26)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.