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