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