There are a lot of options for describing something as being the color orange in German, though not all of them may be quite correct in formal writing! The standard form, and easiest to remember since it is identical to English, is the German adjective orange:
Ein Tiger ist... Ein Tier... das orange ist.
A tiger is... An animal... that is orange.
Captions 22-23, Deutschkurs in Blaubeuren - Der RelativsatzPlay Caption
Used together with the noun, you could say ein oranger Tiger or ein oranges Tier. Okay, a tiger is actually orange and black, but eventually the student in this video gets it right!
A second and third adjective that we could use is orangefarben, or less commonly orangenfarben, meaning "orange-colored." In that case our imaginary tiger—missing its black stripes—would be ein orangefarbener or orangenfarbener Tiger. Add to that some other similar fourth and fifth "orange" adjectives and you have ein orangefarbiger or orangenfarbiger Tiger. In the latter, orangefarbig is more common than orangenfarbig.
The sixth and last way to express the color orange is very common in spoken German, but according to the Duden dictionary, orangen is actually slang usage:
Ich glaube, am besten gefällt mir nicht die orangene Farbe.
I think I don't like the orange color best.
Caption 19, „Mini-Marxe“ - In TrierPlay Caption
Der orangene PKW wird auf vierzig Kilometer pro Stunde beschleunigt.
The orange passenger car is accelerated to forty kilometers per hour [twenty-five mph].Play Caption
Orange, orangefarben, orangenfarben, orangefarbig, orangenfarbig, orangen: Find some more examples of "orange" and other colors on Yabla German to see how they are used in a real-world context.