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