Step 1: Understanding what 'cool colour' means
Colours are categorized into two main types — warm and cool.
Cool colours are those that remind us of calm, peaceful things like water and sky.
Step 2: Identifying cool colours
Cool colours include Blue, Green, and Purple.
They tend to have a calming effect and are often used in design to create a relaxed feeling.
Step 3: Evaluating each option
(A) Blue $\Rightarrow$ Blue is a classic example of a cool colour.
(B) Yellow $\Rightarrow$ Yellow is a warm colour, associated with sunshine and warmth.
(C) Black $\Rightarrow$ Black is a neutral colour, not specifically warm or cool.
(D) None of these $\Rightarrow$ Incorrect, because Blue is a cool colour.
Conclusion:
Hence, Blue is the correct answer as a typical cool colour.
\[
\boxed{\text{Correct Answer: (A) Blue}}
\]