What is the principle of blue filter?

The filter is made of plastic or glass, and special dyes are added. The red filter only allows red light to pass through, and so on. The refractive index of glass sheet is almost the same as that of air, so it is transparent because all colored light can pass through it. However, after dyeing, the molecular structure changes, the refractive index also changes, and the passage of some colored light also changes. For example, a beam of white light passes through a blue filter and emits a beam of blue light, while green light and red light are very few and most of them are absorbed by the filter. Filters have played a great role. Widely used in photography. Why is the main scene always so prominent in the landscape paintings taken by some photographers? How do you do it? That's what filters are for. For example, if you want to shoot a yellow flower with a blue sky and green leaves as the background, you can't highlight the theme of "yellow flower" because the image of yellow flower is not prominent enough. However, if you put a yellow filter in front of the camera to block the green light emitted by some green leaves and the blue light emitted by the blue sky, and let the yellow light emitted by the yellow flower pass through in large quantities, then the yellow flower will be very obvious and highlight the theme of "yellow flower".