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