Go for deep purple quolots (i prefer quolots better with a-lines). And since u said its casual type dress i wouldnt advice u to really go for an extravagent quolots. If it was formal/party wear i would have suggested u get quolots boders done with black embellishment. But for casual look, just go for plain quolots or u can even try and get them dyed in two colors like coming black to purple.