Enhancing colours

There are many ways. Here is just one.

Starting with this picture of bluebells I found in Google images.

1. Duplicate the Background layer and set the duplicate layer's Blend Mode to Multiply.

This darkens the entire picture, but we will fix that later.

If the result on the bluebells is too extreme, lower the Layer's Opacity, which I did here (55%).

Now to restore everything other than the bluebells.

2. Add a Layers Mask to the duplicate layer. Fill the mask with black to restore the entire original picture.

3. Set the foreground/background color chips to their white & black defaults.

4. Activate the Brush tool with a soft brush. Paint the bluebells with white to reveal the new color.

If you paint too far, for example onto the grass, paint with black to restore the original. You can type "X" to toggle between white and black.

You can get similar results with other Blend Modes such as Color Burn and Linear Burn.