My oranges turn out dark (dirty looking) with hardly any orange pigment left. What can I do.?

I live in south west florida. There is plenty of fruit on the trees but Ugly fruit. I have three trees and they all produce the the same. They almost look to me tobe sunburnt. I am not sure what the type of oranges are. I am asking on behave of my father. He mostly uses them for Juicing. I guess they juice OK. Thank you for any advice