Stop-Gap Humanity Test!

Hi there! Recently, we've become the target of malicious automated web browsing software known as robots or spiders and associated malicious human attackers known as blackhats or douches. In order to combat them and keep our forums clean and fast, we currently require that you answer a question to verify that you are in fact not a robot or blackhat.

Note that if you fail the test below, your IP address will likely be blocked until you personally contact site tech support. However, the test only requires that you be made of flesh and pure of heart. No biggy. Take as much time as you need — the question isn't designed to be difficult, but it was thrown together spur of the moment to reduce the load on the server, so don't feel 'dumb' if the answer isn't immediately obvious.

WARNING: Do NOT disable `cookies` in your browser's settings for this site! Not only are they important to the operation of this test, but also to the functioning of user logins on the forums!

Here's the question: Which of the following can be best described as 'yellow'?