What causes that ?

Orange? Usually food!
But if it doesn't come off with a toothbrush, you could have candidasis or oral thrush - a fungus, often from too much mouthwash or antibiotics. It can mean poor digestion.
Try a natural mouthwash of vinegar and maybe some crushed garlic even though your breath may be garlicky, and scrub your tongue with a toothbrush.

The Chinese have used the appearance of the tongue to diagnose for thousands of years. Your tongue shouldn't be so pink-red that it looks raw. It should have a tiny coating of white but be mainly a healthy average pink overall.

Yes I have been using mouth wash the clear crest a lot I think that probably it.