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