I'll create another layer for the clouds, set the blending mode to "Color" and opacity to 50%.



I'll pick an off white color from the "Color Picker" for the clouds.



I'm done painting the clouds.



You can make adjustments to the color in each layer. First you need to select everything in the layer by "Ctrl-clicking" on the layer icon of the layer. The layer icon is a scaled down image representation of the layer. It is the icon to the right of the eye and the left of the layer name. It just looks like a scaled down version of what's in that layer. Hold down the "Ctrl" button on your keyboard and left click the layer icon. You will know that you have selected everything in the layer if you see a selection marquee(marching ants) around the part of the image that is in the layer. See how "The Mittens" is surrounded in a selection marquee in the screen shot below? That's because I "Ctrl-clicked" the layer icon with "The Mittens" coloring in it. You can hide the marching ants, but keep the selection, by hitting "Ctrl-H." This is helpful when you make adjustments and don't want to see the marching ants. You can press "Ctrl-H" to un hide it.