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