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