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