[Tamlin]

The only problem is that coloured filters like red, green and blue are usually only used in black & white photography. For example, a red or yellow filter is generally used to make the blue of a sky dark and thereby accentuate any clouds (in other words, the red/yellow filter blocks the blue light, causing blue areas to be underexposed and therefore appear darker on monochrome film). Green filters lighten foliage, since they allow through more of the green light reflecting off leaves and grass, resulting in a relative overexposure (and therefore lighter tone) in the green areas.

Unfortunately, this doesn't translate directly to colour photography. The sorts of colour filters used in colour photography (such as the 81 warming range and the 82 cooling range) are much less aggressive that B&W coloured filters, and are generally used for light balancing or colour compensation.

So yes, if you take a colour photograph of a yellow banana with a green filter, the banana will turn out green. Unfortunately, so will everything else in the picture.

Oh, and yes, those Cokin filters are still available if you're interested.