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