What are those color filters for SLR lenses? (Red, orange, blue, purple. . . . . . ) The red filter can improve the red color.

It should be said that reducing the transmittance of other colors except red can enhance the red color of the picture and create a special effect. There is also a color gradient lens, which is often used to change the color of the sky in landscape photography. However, with the popularization of digital darkroom technology, these effects can be completely accomplished by Photoshop. If it's not a photo contest or the nature of work requires that digital stickers can't be used, there is no need to buy color filters specially.