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)(11,18)(12,16)(13,17)(14,15)(19,20)(21,23)(22,24)(26,29)(27,35)(28,38)(34,40)(2,6)(3,7)(10,15)(11,17)(16,23)(19,24)(25,26,31,29)(27,36,35,32)(28,39,38,33)(30,34,37,40)(1,3)(2,4)(5,7)(6,8)(25,27)(26,32)(28,37)(29,36)(30,38)(31,35)(33,40)(34,39) involution — undirected(1,4)(2,3)(5,8)(6,7)(9,11)(10,13)(12,19)(14,17)(15,18)(16,22)(20,23)(21,24)(25,28,31,38)(26,33,29,39)(27,37,35,30)(32,40,36,34)(9,12)(10,16)(11,19)(13,22)(14,21)(15,23)(17,24)(18,20)(25,29,31,26)(27,36,35,32)(28,39,38,33)(30,40,37,34)(9,13)(10,17)(11,15)(12,20)(14,18)(16,19)(21,22)(23,24)(25,30,31,37)(26,34,29,40)(27,38,35,28)(32,39,36,33)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.