Step 1: Understanding Transparency in Colours.
Watercolour is known for its transparency. It allows the white of the paper to show through and is often used for creating light, transparent washes. In contrast, oil and poster colours are opaque, and pastel colours can be applied in layers to create texture, but they are less transparent than watercolour.
Step 2: Verifying the Options.
- Option (1): Watercolour is the most transparent of all, making this the correct answer.
- Option (2): Poster colours are generally opaque.
- Option (3): Pastel colours are not as transparent as watercolour.
- Option (4): Oil colours are opaque and not transparent.
Conclusion:
Therefore, the correct answer is (1) Watercolour.