Is stuff like blendcolor and blendalpha expensive

Just checking some stuff out ... I have some sprites (missiles) that are white and stuffed into a pool. I then have different datablocks that represent different missile types and I use the blendcolor funtion to change the color (red, green, blue etc) of the missile sprite when it comes out of the pool. My question ... is this (setBlendAlpha) an expensive operation i.e. repeated every frame by the gfx chip or is it a one off? Same goes for setBlendAlpha?

Cheers