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