Step 1: Understanding Transparency in Colour Mediums.
The transparency of a colour medium refers to how much light passes through the medium and how much the surface beneath can be seen. Some painting mediums allow for more transparency, while others are more opaque.
Step 2: Evaluating the Options.
- Option (1): Poster paints are typically opaque and not transparent.
- Option (2): Oil paints are known for their opacity, but they can be diluted to allow some transparency.
- Option (3): Watercolours are highly transparent. When applied thinly, they allow light to pass through, creating a transparent effect.
- Option (4): Pencils are not considered a colour medium that involves transparency in the same way as paints.
Conclusion:
Therefore, the correct answer is (3) Watercolour, as it is the most transparent colour medium.