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