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