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