Yes, blue is a Scrabble word!

Verb

1. Turn blue

Adjective

1. Of the color intermediate between green and violet; having a color similar to that of a clear unclouded sky

2. Used to signify the Union forces in the American Civil War (who wore blue uniforms)

3. Filled with melancholy and despondency

4. Characterized by profanity or cursing

5. Suggestive of sexual impropriety

6. Belonging to or characteristic of the nobility or aristocracy

7. Morally rigorous and strict

8. Causing dejection

Noun

1. Blue color or pigment; resembling the color of the clear sky in the daytime

2. Blue clothing

3. Any organization or party whose uniforms or badges are blue

4. The sky as viewed during daylight

5. Used to whiten laundry or hair or give it a bluish tinge

6. The sodium salt of amobarbital that is used as a barbiturate; used as a sedative and a hypnotic

7. Any of numerous small butterflies of the family Lycaenidae