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