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