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