Let's add a little noise to the image to help the two photos blend more seamlessly together. Go up to the Filter menu at the top of the screen.
choose Noise, and then choose Add Noise. This brings up the Add Noise dialog box. Set the Amount to somewhere between 2-6% depending on the pixel dimensions of your image. I'm working on a low resolution image for this tutorial, so I'm going to set mine to 2% just to add a hint of noise. Make sure Distribution is set to Gaussian, and also make sure the Monochromatic option at the very bottom is checked.
Choose the original layer Click on the New Fill Or Adjustment Layer icon at the bottom of the Layers palette.
Then select Solid Color from the top of the list that appears. Photoshop's Color Picker will appear. Choose the color that you want to use for your image. I'm going to select a dark maroon for my color.
Similarly choose dark blue color for the crowd below.
Click OK once you've chosen a color to exit out of the Color Picker. Don't worry about choosing the "right" color at the moment because you can always change it later.
Now choose the desaturated layer. click on the Add A Layer Mask icon at the bottom of the Layers palette:
Select your Gradient tool from the Tools palette, or press G to quickly access it.Then, up in the Options Bar at the top of the screen, click on the down-pointing arrow to the right of the gradient preview area, which will bring up the Gradient Picker. Click on the black to white gradient in the top row, third from the left to select it.
hold down your Shift key and drag out a black to white gradient to blend the two images together. (black hides, white reveals concept of layer masking)