How replace color works

One reason you can't change the colour, is because there is no colour to change.  Using the Color Picker tool we see a perfect light grey at position #1 and the merest hint of red at position #2 (which is what D Fosse told you)

When we attempt to adjust colour in Photoshop, it does not affect full black and full white, and has the most effect at a mid grey.  The layer filled with red and set to Color overlays a black to white gradient, and demonstrates  where it is working and where it has no effect.

That's correct. "Color" in Photoshop has a narrower and more precise meaning than it does in everyday speech.

In Photoshop, you need to make a distinction between Color and Luminance. In your example, you want to change the luminance component, not the color component. In fact, the white wall doesn't have any color at all.

White > Gray > Black are not colors, they are the complete absence of color. It's the luminance scale. Hence, Replace Color is not applicable here as the others say.

What you need to do is to select the area you want to modify, and make a mask in an adjustment layer that allows you to do what you want (Curves or Levels).

Probaría seleccionando el área a oscurecer. Y Ajustes/ Corrección selectiva, elegir blanco y desplazar el negro hacia la derecha hasta tu objetivo de oscurecimiento... O hacer lo que dice Fosse, también

In my experience Replace Color is worthless for serious work because it is destructive. 

It generally affects color – not luminance. 

The problem being that »color« has some variety of meaning, but here it roughly refers to a combination hue and saturation. 

I would recommend using Adjustment Layers.