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