Your camera might be able to get the white balance right internally, rather than fixing it later. Even the cheapest usually have 'daylight' versus 'indoors' modes, and a lot of cameras have a manual white-balance mode, where you take an image of a white featureless area (wall, paper, etc), and tell it to treat that colour as 'white'.

I suspect you'll have less luck with the filter - unless it's _really_ thin, it'll change the focus when you insert it. You'll need to mount it carefully, so it doesn't block all the magic sensors (ultrasonic distance meter for focussing, ambient light sensor, etc).