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