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