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