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