Here is how it works. First open an image
In this case I want to make the water a little blueish. So i add a Solid color Adjustment layer and choose a light blue color
Change its blending mode to Color.
Now the picture is completely blue. So fill mask with black and paint with a soft white brush over the water. Lower the Opacity of the layer and you get this.
You add more sold color adjustments layer and fill it with other colors to give other parts of your picture also some color.
Cool and simple ! And by double clicking on the solid color you can easily change the color.