A very valid point! I painted my vanilla marines as Howling Griffons as I felt subtlety was not the point of wearing Power Armour.
Yup is why I love my Imperial Fists. We go to war in bright yellow armour because we WANT our opponents to see us and know who's come to to kick their arse! We're Space Marines and we don't do subtle!
Either there is life in the universe more intelligent than us, or we are the most intelligent form of life in the universe. Either way, it's a worrying thought!