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