In design, color matters! And reducing the number of colors by harmonizing them gives a slide more impact. You are therefore better off choosing your font color from one of the existing background colors, like in the slide on the right, than using a basic color, like the white in the slide on the left.
To do this, you must first pick a color on the background photo. You will need a “color picker” for this; there are many free color pickers, such as Color Cop, which you can download at this address: http://colorcop.net/
Color Cop lets you select a color directly on the screen using an eyedropper, and shows it in a window, along with its RGB (Red-Green-Blue) code. You can use a magnifier for easier selection:
Just drag the eyedropper over to the selected color in your picture and the code appears in the Color Cop window:
… then copy the RGB code shown in Color Cop into the corresponding area of the PowerPoint window:
… to create the desired effect:
See this news in French: http://presentations-de-vente.com/assortir-la-couleur-de-la-police-a-limage