I like to use Cokin's 036 FL-W (for "fluorescent light - white"; its colour is sort of purple) filter for urban night photography. It is very effective in correcting the greenish tones produced by the sort of fluorescent lighting found in most streets and public areas. I would like to use the same colour correction on a Canon 15mm fish-eye lens, which will only accept a gelatin filter in a filter holder at the back of the lens. Any idea what filter would do the job? I suspect the filter holder will only take one filter, two will probably be too thick to fit. Does any single filter give a good colour correction for fluorescent light? I have tried FL-D (fluorescent light-daylight) filters before (Cokin, B+W) but they do not efficiently counter the strong overall green tone of night sceness in the city.