This is a famous test in cognitive psychology called the Stroop task (named after the psychologist John Stroop who first studied it).
The fact you were slowed down – or made errors – while trying not to let the meaning of the words interfere with your ability to say out loud the colours – is called the Stroop effect .
Look again at the figure. In the first two lines, there should have been no problem in naming the colours – because the meaning of the words and the colours match. But in the next lines, the meaning of the words and the colours are a mismatch – there is a conflict and this causes the problem, slowing you down and causing errors.
What explains the Stroop effect? The effect can be explained by the conflict between two types of information processing: a type of information processing that is automatic and effortless i.e. reading the words – something you have done countless times; and a type of information processing that requires deliberate selective attention to information that is unusual (naming the colours), while suppressing interference from automatic, well learned response to the word meaning.
The ability to flexibly attend to different aspects of our world in ways that are not routine or automatic is essential to fluid intelligence. You cannot use your fluid intelligence on autopilot. And there is good evidence that your fluid intelligence is closely related to your ability to stay on track in a task or while pursuing a goal – and not to get distracted by interfering information or automatic modes of thinking or behaving that don’t help you attain your goal.