Coloring colored ice-cream
If you make homemade strawberry ice cream, the color is likely to be very, very pale, approaching white.  Green food coloring in your mix should do the trick.  

It would be very difficult to retroactively turn commercial ice cream a different color.  The pink is almost certainly from food coloring, and mixing in another coloring would be very difficult without adversely affecting the texture of the ice cream--essentially you would end up having to melt and rechurn, to get any kind of decent result, in which case you might as well simply make homemade ice cream.

You can get recipes very easily by googling.  You will, of course, need an ice cream maker.  The frozeen barrel kind can be had readily and for a reasonable price.