I'd like to mention another option in the paint arena: POR-15
You can have it any color so long as its BLACK
You cant paint over it.
It seals so your bike wont ever rust where its been painted.
You probably cant remove it without loss of blood.

Car Restoration people use this stuff for serious rust prevention on sensitive old steels (old italian steels are notorious)

Its not something to do to your colnago, but your winter bike will last forever painted with this stuff.