If u dont have gimp,you can download it here.
download the original image from here.
In my example i have two layers in my layers palet
1. A background layer that is named background.there is a red car in this pic that will be our subjek.
2.Duplicate the background layer and desatured it.Colors>Desature.
3.Then create a new layer mask.Select background copy layer and right click>Add layer mask.
4.Initialize layer mask to white(full opacity).click Add.
I named my background copy layer to Layer 1.(I always renamed my layer so it is easier to me to remember the layer rather than named the layer copy)
You will notice a white image layer on the right side of our Layer 1.That is our layer mask.
5.Then pick brush tool.Select circle brush size 19.Then scale the brush to 10.Make sure our foreground color is black.
6.Then apply the brush and start painting the car at layer 1.You’ll see something like this:
You'll see that we will colorize back our car to red.dont worried about being perfect because nothing is being deleted. It’s all there.Just switch between black and white and you can fix your mistakes.
So remember black will hide our desature layer.and if u delete the layer mask u will get back the desture layer.
This is my final result using layer mask.
hope this tutorial will help some beginner user to understand how to use Layer Mask instead of erasing the layer.
some other related gimp tutorial on layer mask;
Selective color on Open Source Photography (OSP)
Layer Mask Fun With Gimp