Next step: the atmosphere.

The atmosphere is usually done with soft low flow or opacity brush. It helps to knock out objects into the distance and VS. You should know what the value is on this step; if you do it will really help. In 2 words Value: is the degree of Importance.

And if not in 2 words read this:

Value is a measure of where a particular color lies along the lightness-darkness axis. A color's value is its amplitude. Various color models have an explicit term which places the color on a scale from utter black to pure white. The HSV color model and Munsell color model have an explicit value, while the HSL color model uses a related parameter called lightness instead. In the HSV and Munsell color models, a color with a low value is nearly black, while one with a high value is the pure color.

The image shows three hues in the Munsell color model. Each color differs in value from top to bottom in equal perception steps. The right column undergoes a dramatic change in perceived color. In subtractive color, i.e. paints, value changes can be achieved by adding black or white to the color. However, this also reduces saturation.

Chiaroscuro and Tenebrism both take advantage of dramatic contrasts of value to heighten drama in art. Artists may also employ shading, subtle manipulation of value.

So, to knock out my background architectural place along with the mountain
  
I will use soft brush with light blue color.

Matte painting

The whole view:

Matte painting

I've also decided to put t a very strong element to my foreground.

Matte painting

The final steps: color adjustments and layer merging. First merge all the Photo layers.

Matte painting

Adjust the color first with Hue/saturation adjustment.

Matte painting

Erase the areas in the sky with soft low flow brush. This way we will get something like ascended sun rays coming from the sky.

Matte painting

Colors balance the picture and we are ready here:

Matte painting

So here is our final matte painting, it is my first practice on these kings of techniques, so that means more mattes to come. I really hope you've learned at least some methods and tricks.

Matte painting

Hope to see you soon. !