In the following question, names of colours are given. Select the colour that is different from the other three (odd one out).

Introduction / Context:
This verbal reasoning question tests basic knowledge of colours and the ability to classify them logically. Odd one out questions about colours are common in aptitude tests because they combine simple general knowledge with pattern recognition. The focus here is on identifying which colour does not belong to the same natural group as the others, based on well known colour properties.

Given Data / Assumptions:
- The five options are Red, Brown, Green, Yellow, and Blue.
- All are common colour names used in daily life and in basic school level science.
- We consider the standard rainbow or spectrum colours, often remembered as a set of pure hues.
- Exactly one colour does not behave like a pure spectrum colour in the way the others do.

Concept / Approach:
Many exam questions use the idea of pure spectrum colours, which are the colours that appear in a prism or a rainbow. Typical examples include Red, Orange, Yellow, Green, Blue, Indigo, and Violet. Brown, however, is usually treated as a mixture or a shade rather than a pure spectral colour. Therefore, a natural approach is to separate spectrum colours from mixed or derived colours and see which option does not fit the spectral group.

Step-by-Step Solution:
Step 1: Identify which of the options are commonly regarded as spectrum colours. Red, Yellow, Green, and Blue all appear in the standard rainbow list.Step 2: Recognise that Brown is not part of the typical spectrum sequence. It is formed by mixing other colours, often including red and green or other combinations.Step 3: Group Red, Yellow, Green, and Blue together as pure or primary and secondary spectral hues.Step 4: Observe that Brown is fundamentally different in that it is a composite shade rather than a pure spectral hue.Step 5: Since exactly one option is a non spectral, mixed shade while the others are well known spectrum colours, Brown is the odd one out.

Verification / Alternative Check:
Another way to verify is to recall that in school level science demonstrations, when white light passes through a prism, colours like Red, Yellow, Green, and Blue appear in order, but Brown does not appear as a distinct band. Brown is produced by combining other colours and usually needs a context such as a darker background or surrounding colours. The fact that Brown relies on mixing, whereas the others stand alone as spectral hues, confirms it as the odd one out in this list.

Why Other Options Are Wrong:
Red is not the odd one out because it is a core spectrum colour and groups naturally with Yellow, Green, and Blue. Green is also a key spectrum colour and often used as a primary colour in digital displays. Yellow appears prominently in the rainbow and therefore belongs in the same group. Blue is another fundamental spectrum colour seen both in the rainbow and in basic colour theory. Each of these four shares the property of being a pure spectral hue, so none of them can be classified as the odd one out here.

Common Pitfalls:
Sometimes test takers may think of frequency or psychological impact and overcomplicate the pattern. Others may decide that Yellow is odd because it appears brighter, which is subjective. In reasoning questions, the expected solution is usually based on clear, objective categories, such as spectral versus non spectral colours. Remember to look for standard scientific or widely taught groupings rather than personal impressions of brightness or preference.

Final Answer:
Brown