How to Remove All Colors But One in Photoshop
Use the Adobe Photoshop software to turn a full-color image to a black and white, or grayscale, picture with just a few clicks, with no special settings on the camera required. Photoshop also offers the ability to create images using spot color, which is where you pick and choose the colors to include and convert the rest of the image to grayscale. Spot color can be a striking effect when you select a single color to bring out from the image.
Open Adobe Photoshop, click the "File" menu and select "Open." Locate the photo to change and double-click its file name, opening it on the Photoshop canvas.
Click the "Select" menu at the top of the screen. Click "Color Range." Click the "Image" radio button if it is not already selected below the picture preview.
Hover the cursor over the picture preview. The cursor turns into the "Eyedropper" tool. Click the color on the picture to save when the rest of the colors are removed.
Click the "OK" button to close the window and return to the image. Note that parts of the image are now surrounded by blinking dotted lines. This may be a very small area or large parts of the picture, depending on your chosen color.
Right-click inside the blinking dotted lines and select "Layer via Copy." A new Layer 1 is added to the "Layers" palette on the right side of the screen.
Click the Background layer below Layer 1. Pull down the "Image" menu, click "Adjustments" and select "Hue/Saturation." Slide the "Saturation" bar all the way to the left, removing all the color from the picture except the selected areas. Click the "OK" button.
Click the small lines icon at the top-right of the "Layers" palette. Select "Flatten Image" and the two layers combine down into one. Click the "File" menu and select "Save As." Type a new name for the picture, to preserve the original full-color version, and click the "Save" button.