The question remains on how difficult would it have been for them to maintain their same color. This is hardly original. They're already godly with the Soul Dew, they hardly need megas. For a Latios one, it would be really good but Latias is supposed to have that feminine grace about her and a distinctive color.
Well, was it original that they have basically the same animations in battle even in their normal forms? I mean, why get caught up in the color if it makes sense that twins (in real life even) would be the same color anyway? The combination of their normal colors, no less. I think it's kinda clever that they emphasize the idea of them being twins, even if it looks unoriginal.