Photoshop how to blend image with solid colors

Question

I was watching a video and in the background, the guy was demonstrating his photoshop skills in a timelapse. I am trying to figure out how he achieved this particular blending effect. I went frame by frame through the video but it is just too fast. I included a photo of the image before and after. I spotted that he was using "blend layer" and "color overlay". Could someone explain to me or point me in the right direction as to how to achieve this particular effect. Note the original image is on the right.

Answer 1

Gradient Map most likely.

The color overlay may be secondary and not the overall factor.

Answer 2

I'm writing an answer which also uses Gradient Map but I managed to figure out a way for those high contrast effect can be created. In case you or someone else find it helpful:

The high contrast can be achieved using Blend If [Gray] option in Blending Options. Here are the steps to create a very similar result:

1. Make a selection of the image and convert it into smart object and keep it as a separate layer (Layer 1).

2. Bright / Transparent area: Go to Blending Options of this layer and adjust the slider like this (basically it will hide the brightest areas, depending on the amount of slider):

   

   As you can see, background is visible now, through the photo.

3. Dark area: Then create a Solid Color layer (Layer 2) with black color on top of Layer 1. And change its Blend If values like shown below. Note that this time I've changed the slider for Underlying Layer, which is Layer 1.

   Basically, it will remove the parts of solid black layer which are right above the brightest areas of layer (Layer 1) below it.

   

   Another thing to note (in case you're new to Blend If feature) that you can split each slider into two parts and it will give you smoother blending. You can experiment if you want. To split it, you can hold Alt key while you drag slider. But for this answer's purpose, it's not really necessary.

   We'll have this result after 3 steps:

   

4. The Flat Blue Color: Now we'll use Gradient Map. Group Layer 1 and Layer 2. Create a new Gradient Map adjustment layer with sliders like this:

   

   The darker color would be the darkest color in our final result, the blue color would be the flat blue color. You can choose colors of your choice.

   Now use it for a Clipping Mask with the group below it. (you can use Alt + Click method to do so). You should get this:

   

5. Making body/face bright: Right now, we are seeing background through the body or face of the person. So we can create a solid bright color layer just below the Layer 1 and Layer 2 group. Then mask it so it only shows behind the body figure. You can use the Layer 1 for making a quick selection and masking. Something like this:

   

   Layers Panel:

   

The final result should look like this:

You can now simply use Hue/Saturation layer for more colors: