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