General Synonyms:
* Dismal
* Gloomy
* Depressing
* Desolate
* Hopeless
* Cheerless
* Unpromising
* Grim
* Barren
* Sterile
Synonyms Emphasizing Lack of Hope:
* Despairing
* Dejected
* Disheartening
* Fatalistic
* Pessimistic
Synonyms Emphasizing Lack of Comfort:
* Unpleasant
* Unwelcoming
* Austere
* Sparse
* Uninviting
Synonyms Emphasizing Lack of Color or Light:
* Gray
* Dull
* Somber
* Monotonous
The best synonym to use will depend on the specific context of your sentence and the nuance you want to convey.