You can only change the color of single-colored icons, text and lines. The color of Photos cannot be changed.
To do so, first click to select the graphic element(s) for which you would like to change the color. Next, click on the bucket of paint icon located at the top menu.
You can then change the color of the graphic element by pasting a hex code, choosing a default color, or clicking the + sign under Recent Colors to choose from a color palette.
Then you can easily choose from a range of color and gradients. The 5 recently used colors will appear in "Recent Colors" after selecting it.
Kindly note that you won't be able to change the color of multi-colored icons. This is because they contain more than one color tone, texture, and gradient.