When you upload your photos from your Camera Roll, Facebook compresses your content which can darken your cards and make them look gray. Our first suggestion would be to post directly from the app.
If you choose to post from your camera roll you can revert the filter back to the Original filter. To do this after uploading :: 1. Tap on card to open the editing bar 2. Tap on "Filters" 3. Tap on "Original" and your card should be back to the original...or choose one of the other filters for a more artistic look!
Questions? Just email us at firstname.lastname@example.org