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