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