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