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