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