How to stop paint from making the above paint darker when painting behind?

[itsallaboutp]

The blue is what I need behind it. I can just erase the dark part on the blues layer but is there another way? Because this can take long and also cause me to have to go back and color over again.

The blue is the sky and the other color is sand I am trying to just paint the rest of the sky so I don't have a white spot there. I know about blend modes like add but it doesn't work with this. This case I need it behind without making the above color layer dark when they blend. (the two colors are in different layers)