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