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)(13,18,21,16)(20,22,24,23)(25,26,30,33)(27,28,31,35)(29,37,38,32)(34,40,39,36)(1,2,4,5)(3,6,7,8)(9,10,14,11)(12,17,19,15)(13,16,21,18)(20,23,24,22)(27,31)(28,35)(34,39)(36,40)(10,11)(12,19)(16,18)(20,24)(25,27)(26,28)(29,34)(30,31)(32,36)(33,35)(37,40)(38,39) involution — undirected(9,11,14,10)(12,17,19,15)(13,18,21,16)(20,23,24,22)(1,3,4,7)(2,6,5,8)(9,12)(10,15)(11,17)(13,20)(14,19)(16,22)(18,23)(21,24)(25,28)(26,31)(27,33)(29,36)(30,35)(32,39)(34,37)(38,40)(9,13,14,21)(10,16,11,18)(12,20,19,24)(15,22,17,23)(25,29,30,38)(26,32,33,37)(27,34,31,39)(28,36,35,40)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.