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