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