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