Learn Spanish (Latin America): Nuestra casa es blanca.

In Spanish, the word for "our" must match the gender of the thing being owned, not the gender of the people who own it. Because casa (house) is a feminine word, we use the feminine nuestra. You use this even if the house belongs exclusively to a group of men!

Since "our" means more than one person, why isn't it nuestras?

Just like with gender, the singular or plural form of "our" depends on the thing you own, not how many people own it. Since there is only one casa (singular), we use the singular nuestra. If the family owned multiple houses, it would be nuestras casas.

Why do we use es instead of está?

Both words mean "is", but we use es (from the verb ser) when talking about permanent or defining characteristics. The physical color of a house is considered a basic, lasting trait, so we use es.

Why does the word for white (blanca) end in an "a"?

Descriptive words (adjectives) always have to match the gender of the noun they describe. Since casa is a feminine noun, the basic dictionary word for white (blanco) changes its ending to match, becoming blanca.