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