Use a gradient map adjustment layer to quickly amp up the vibrancy or posterize your image

1. In the Layers panel, click create new fill or adjustment layer icon and choose Gradient Map to open the Properties panel.
2. Click the gradient preview drop down to open the Gradient Editor
3. Choose a basic duotone with 2 colors
4. To change colors, click the gradient preview, then double click on a Color Stop to open the color picker and select your desired hue. Click OK.
5. Adjust each Color Stop as needed.
6. Adjust the balance between colors by dragging a Color Stop or Color Midpoint to a new position on the spectrum.
7. Add Color Stops to the map by clicking directly underneath the gradient and edit as needed.
8. Click New to save a gradient. Click OK when finished.