Step 4: Make Sure "Snap To Guides" Is Turned On

In a moment, we're going to begin dragging selections around our four sections using the Rectangular Marquee Tool, and to make things easier for us, Photoshop is going to snap our selections directly to the guides we've created. Or at least, it will if we have the Snap To Guides option enabled. Go up to the View menu at the top of the screen and select Snap To. A submenu will appear with the Guides option at the very top of it. Look to the left of the word "Guides". If you see a checkmark beside the word, it means the option is already enabled so there's no need to select it. If you don't see a checkmark, click on the word "Guides" to enable to option:

Step 5: Select The Rectangular Marquee Tool

We can now begin dragging a selection around our first section. Grab the Rectangular Marquee Tool from the top of the Tools palette, or simply press the letter M on your keyboard to select it with the shortcut:

Step 6: Drag A Selection Around The First Section On The Left

With the Rectangular Marquee Tool chosen, start in the top left corner of the photo and drag a selection around the first section on the left of the image. You'll notice that as you move close to the first guide, the selection will snap to it thanks to that Snap To Guides option we enabled. If you find it difficult to place your cursor in the top left corner of the image while working in a document window, press the letter F on your keyboard to switch to Full Screen mode, then drag the selection. It's a bit hard to see in the screenshot, but when you're done, you should have a selection around the entire first section of the image:

Step 7: Add A Hue/Saturation Adjustment Layer

With the selection active, click on the New Adjustment Layer icon at the bottom of the Layers palette and choose a Hue/Saturation adjustment layer from the list:

This brings up the Hue/Saturation dialog box. Before we do anything with it though, let's take a quick look at what's happened in the Layers palette. We now have a Hue/Saturation adjustment layer sitting above our image on the Background layer, but more importantly, look at the layer mask preview thumbnail on the right of the adjustment layer. Notice how it's filled with black except for a white section on the left:

That's because we added the adjustment layer while we had a selection active in the document. Photoshop used the selection to alter the adjustment layer's mask. The white section on the left is the area we selected in our image, and the white means that whatever we do with our Hue/Saturation adjustment layer will be visible in that section of the image. The rest of the layer mask is black, which means that the rest of the image will not be affected by anything we do with our adjustment layer. This is what's going to allow us to colorize each section independently of the others.

If you want to learn more about how layer masks work, be sure to check out our full Understanding Layer Masks tutorial in the Photoshop Basics section of the website.

Step 8: Select The "Colorize" Option In The Hue/Saturation Dialog Box

Now that we've taken a look at the Layers palette, let's use the Hue/Saturation dialog box to colorize our first section. First, we need to tell Photoshop that we want to colorize the image, so select the Colorize option in the bottom right corner of the dialog box:

Step 9: Choose A Color With The Hue Slider

With the Colorize option selected, choose whichever color you want to use by dragging the Hue slider either left or right while keeping an eye on your image until you find the color you want to use. The default color is red, which I think works well with my image, so I'm going to simply leave the Hue slider alone for now and accept the default color. Of course, you may want to choose a different color for your image:

Click OK once you've found the color you want to use to exit out of the Hue/Saturation dialog box. If we look at the image in the document window, we can see that the first section on the left is now colorized with the chosen color:

Step 10: Change The Blend Mode Of The Adjustment Layer To "Color"

Let's make sure we're affecting only the color in the image, not the brightness (luminosity) values. For that, all we need to do is change the blend mode of the adjustment layer. You'll find the layer blend mode options in the top left corner of the Layers palette. By default, layers are set to the "Normal" blend mode. Change the blend mode to Color:

The difference to your image may be subtle depending on the color you've chosen, but now we know for certain that we're changing only the color in the image. Whatever color we choose will not affect the brightness values. Here's my image after changing the blend mode to Color:

One section down, three to go!