Open up a full colour image in Photoshop. I’m using a town scene from my photo gallery:
Go to Layer > Duplicate Layer and click Ok.
Go to Image > Adjustments > Hue/Saturation and set the Saturation to -100, as below:
Once you hit Ok, you should have a black and white image:
In the tool menu, click the Eraser icon and carefully click and rub over the parts of the image you want to ‘pop’. You can adjust the size and strength of the eraser in the menu bar, and it will also help if you zoom in to see what you’re doing.
Once you’ve carefully coloured everything you want to stand out, save and you’re done: