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