Saturation control-black and white

It can be seen from Figure 1 that even different colors may have the same performance after being converted to black and

white, which makes it difficult to demarcate the relationship between the images in the picture.

▲From Figure 1, after turning to black and white, the two colors turned out to be the same gray.
▲From Figure 2, after remove the color, the level of the black and white photo depends on the brightness.
▲From Figure 3, After removing the color, the visual focus is completely different. The color brings different effects to the
picture. Is it the key or redundant? Black and white layering, saturated color picture, which one can enrich the picture more?