How to change object color using color picker?

How to change color of a wall on mouse click, choosing color from color wheel ?

In game or in editor?

in editor you can modify the material colour (assuming the material shader has a colour tint value).

in game? well you would need to build a colour picker (could be as simple as a texture, where you pull the pixel colour of the coordinates you clicked). Then you would need to trigger the picker when the wall is clicked (likely using raycasting the mousepoint into the world to detect the click). and thena gain after all of that, the colour selected would need to be given over to the walls material shader to actually be used.