The TwoTone effect layer allows you to repaint the image with two colors. Add a twotone layer by clicking the Two Tone icon on the Effects drop down, then adjust the selected twotone layer in the TwoTone Properties panel.
TwoTone Properties
Color Combination
Select from available preset color combination from the drop down list.
Use the Dark Tone and Light Tone: buttons to use a custom color.
Gradient bar
The gradient bar represents the mapping from a pixel's brightness to a new color.
Dark pixels will be assigned to the color on the left of the gradient.
Light pixels will be assigned to the color on the right of the gradient.
The sliders under the gradient bar are known as Markers.
Select a marker by clicking on it. The selected marker will be shown as a white slider with a black outline.
You can move the selected marker's position in the gradient by dragging it.
You can change the colors with the Dark Tone and Light Tone buttons.