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