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