Well, actually the texture of the red sails does have shadows and structure at the same degree as the other sails. But perhaps the red ist a too strong color, so it isn't visible. Well, you can't allways win, I guess. I just thought might be interesting to try something new.
Personally I prefer the whaf-if-units both as a modder and a player. As a player I prefer what-if-units in general for those civs which have vanished somewhere in history. Sure, on the same land do live other civs today, but they don't have the same culture. If Rome never would been capture for example, I don't think todays roman soldiers or vehicles would look the same as italien does look. Especially if you think about how much Rome did influence europe. Even nowadays there are these influences, so just imagine how strong they would be, if the ancient Rome would still exist. So I like to imagine what those units, the buildings and so on would look like.
And as a modder I must confess, that it becomes boring to retexture the same units over and over again.
But I see, I will better do no more experiments.