To change the color, click on the image to activate a handy toolbox on the screen.
The toolbox allows you to adjust the image, frame, drop shadow, and add text to your layout.
When you click on the small red box in the center of the toolbox, the Image Toolbox is activated.
The Image toolbox gives you access to image controls such as image opacity, brightness, contrast, and blur.
You can also change the color by adjusting the values here. After adjusting the color values, adjust the brightness and contrast until you achieve the color you want.
Other resources for FF users:
LumaPix has some great video tutorials here: LumaPix Video Tutorials
And a helpful forum here: Fot******* Forum