Referring to the given color, here is the result set to normal at 100% blending.

And this is the result set to normal at about 75% opacity.

Step 15

In this step, we will still add some more shade on the area around foreground walls and floor. Create another new layer (Shift+Ctrl+N) above the previous shade layer. Take the gradient tool. Set foreground color to black. Choose a linear gradient set to above 10-15% opacity. Click-hold and drag the tool from the lower bottom upward as indicated by the orange arrow.

Here is the gradient as a reference.

Given this color reference, the result should be like the one in the screenshot. Select the shade layers and hit Ctrl+G to group them in a folder.

Step 16

Proceed to create again a new layer above the shade folder. On this layer, paint a straight thin white line on the edges of the left and right wall. These lines will soften the edge of the wall.

Step 17

Finally we will add ‘a life’ to the scene by placing a model at the edge point of the entrance. We will use this model for this purpose. Cut out the model from this image.

Add the cut out to the main document. Flip horizontally and scale down the size as needed. Set this model layer to normal at about 75% opacity.

Step 18

Next we will add two more color adjustments for the entire scene. On the topmost position, create new adjustment layer (layer > new adjustment layers) and choose a selective color:

Another new adjustment layer: brightness/contrast.

Mask areas around the entrance, left wall, and floor as indicated in red highlight.

Step 19

Create a new layer again (Shift+Ctrl+N) above the two adjustment layers. Take a very soft round brush at low opacity of about 10-15% opacity. Set this new layer to overlay blending at 100% opacity. On this new layer, paint soft white color to define casted light as pointed with an orange arrow.

Step 20

To add the feel of sci-fi, we will add some light flares on the wall and floor. To do this we will paint the light flares. We do this on a separate document. Create another new document (Ctrl+N) with size given below: