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