Lee 4x4" CC25C (Cyan) Color Compensating (Color Correction) Filters act specifically on relatively narrow bands of color. That is why they do not come in two color variants (bluish and reddish) like conversion filters do. Instead, they come in three primary additive colors and their three secondary colors (which can be interpreted as the primary colors of subtractive mixing)—each color comes in practical density steps.
Lee color compensating filters are made in the following increasing densities: 0.025(CC025), 0.05(CC05), 0.10(CC10), 0.15(CC15), 0.20(CC20), 0.25(CC25), 0.30(CC30), 0.40(CC40), 0.50(CC50). You can sandwich as many as three Lee polyester filters together without a noticeable loss of image quality.
Some photographic situations require specific color corrections. For example, when shooting daylight film under fluorescent lighting, some magenta correction is needed in order to remove the greenish tint that would otherwise appear. The amount of color correction required is most accurately measured via a color temperature meter.