Color words in Spanish must agree in gender with the nouns they describe, just like other adjectives. Most colors change their final vowel: rojo becomes roja for feminine nouns, amarillo becomes amarilla, blanco becomes blanca, negro becomes negra, and morado becomes morada. A few colors are invariable: Azul and Verde stay the same regardless of the noun's gender, and Naranja, the most common word for orange, also does not change. As an alternative, Anaranjado or Anaranjada can be used when you want a clearly adjectival form, and Púrpura is a less common alternative for purple.
Articles in Spanish come in two main families. The definite articles, meaning "the," are el for masculine singular nouns, la for feminine singular nouns, los for masculine plural nouns, and las for feminine plural nouns. So el libro is "the book," la casa is "the house," los libros is "the books," and las casas is "the houses." The indefinite articles, meaning "a" or "an," follow the same gender split: un for masculine singular, as in un perro ("a dog"), and una for feminine singular, as in una mesa ("a table").