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