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)(25,26,28,32,29,31,35,38)(27,30,34,36,33,37,39,40)(1,3,4,8)(2,5,6,7)(10,15)(16,23)(17,18)(19,24)(3,8)(5,7)(9,11)(10,16)(12,20)(13,21)(14,22)(15,23)(17,19)(18,24)(25,27)(26,30)(28,34)(29,33)(31,37)(32,36)(35,39)(38,40) involution — undirected(2,6)(5,7)(9,12,13,14)(10,17,15,18)(11,20,21,22)(16,19,23,24)(26,31)(27,33)(32,38)(34,39)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.