**Neptune and Uranus appear to be which colour?**

The correct answer is option 'C' - Blue.

**Explanation:**

Neptune and Uranus, the two outermost planets in our solar system, both have distinctive blue coloration. Here's a detailed explanation:

**1. Neptune:**

Neptune is the eighth planet from the Sun and is known for its vibrant blue coloration. The blue appearance of Neptune is primarily due to the presence of methane gas in its atmosphere. Methane absorbs red light and reflects blue light, giving the planet its distinct blue hue.

**2. Uranus:**

Uranus, the seventh planet from the Sun, also has a blue coloration. However, the exact cause of its blue color is still not completely understood. Like Neptune, Uranus also contains methane in its atmosphere, which contributes to its bluish appearance. The methane gas absorbs red light and reflects blue light, resulting in the planet's blue color. Additionally, the presence of other atmospheric components, such as hydrogen, helium, and trace amounts of other gases, may also contribute to its blue hue.

**Conclusion:**

In summary, Neptune and Uranus both appear blue in color. This is primarily due to the presence of methane gas in their atmospheres, which absorbs red light and reflects blue light. The exact cause of Uranus' blue color may involve other atmospheric components as well. Understanding the colors of planets helps astronomers study their composition and atmospheric conditions.