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