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