Nosotros somos colombiano - correct or incorrect?

Incorrect

Explanation:

In Spanish, adjectives need to match the noun in gender and quantity. In English you could say "We are Colombian" and "I am Colombian" and both are correct. However in Spanish you would need to say "Nosotros somos colombianos" and "Yo soy colombiano". Adding an "s" to the end of the adjective makes it plural. Also in Spanish there is no need to capitalize adjectives.