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