[yuchi]

Actually it is a very debated argument. Most of the choices about colours are about brand/category recognition.

In my experience designers (and is the role I sometimes have) must understand that visual appearance is nothing if not considered in its context. A blue logo is obviously more obvious (no pun intended) and not revolutionary, but is able to vector the category of the much more fast than an orange one. What does an orange circle on an app logo mean? A blue one is more clearly inserted in the right category.

But I see some more interesting issuess: what does that greenish/blue look that social networks acquired after Facebook and Aqua (oh yeah, that aqua UI) really mean? That green/blue is considered in semiology the color of the death and dead bodies[1]. Do you want YOUR logo to pass THAT semiotic message?

[1]: I have no citations here, I couldn't find one. So take my words as unreliable.