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