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