If the camera is positioned in an extremely shaded area, it is possible the flash is being triggered during the daytime. The camera is not getting enough light to take a color picture. It's most common to experience this in the summer months when the tree canopy is more dense and shades more light. Though the reduced light may cause daytime images to render in black and white, they should still be high quality, crisp and clear. If you're set on capturing color images, it is recommended to reposition the camera where the camera can detect a greater amount of light during the day.
Note: Always position camera facing north to avoid direct sunlight in your shots. This can cause false triggers and make it difficult to see the animal in the image.