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