The color Yellow is popular enough where you may need to know how to say it in Spanish speaking countries. Just like learning the colors Red or Blue, being able to describe something and having to use Yellow may come in handy when you least expect it.

Amarilla (Feminine)
Amarillo (Masculine)
Examples of when to use Yellow in Spanish
Those yellow flowers are beautiful – Esas flores amarillas son hermosas
That yellow sign is telling you to slow down – Ese letrero amarillo te dice que bajes la velocidad