P: Anchor point/point for RGB values

I would like to be able to set a anchor point or point of which the RGB values takes it information from. This would make it easier to adjust images to the RGB values, and not needing to hover over the images all the time. 

I also would like to be able to have more persise editing with the curves tool. such as that you can manually type in your own values to the points on the curve. Or make certain parts bigger, or just be able to make the entire thing bigger somehow. thanks.