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