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