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