So you're more into pink?
Why not pink?
Pink is as good as any other colour.
On windows, when you make an attachment of an icon to a program on the desktop, you can pick the icon in the sequence (multiple icons within a single icon embedded into the exe) or point to a completely new icon thats not within the exe. So you could have 2 icons, one pink, one blue.
I think that letting girls have a pink icon would make the messenger more popular - with the amount of messenger type programs out there it will need all the help it can get. There is no real reason why (on install or in settings) that you could not allow different icon colours.
I don't know enough about linux or the mac to see if its possible to do the same on install there. What do you think?