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