Step 1: Understanding Colour Mixing
When two primary colours mix, they form a secondary colour. Yellow and Blue are both primary colours.
Step 2: Applying the Rule of Colour Mixing
In the subtractive colour model used in painting and visual arts:
Yellow + Blue $\Rightarrow$ Green
This is a well-known rule from basic colour theory. The mixture of yellow and blue pigments gives rise to green due to the way light wavelengths are absorbed and reflected.
Step 3: Eliminating Incorrect Options
- (A) Red: Primary colour, but not formed by yellow + blue
- (C) Orange: Formed by Red + Yellow
- (D) Pink: Usually made from Red + White
Hence, the only valid option is Green.
\[
\boxed{\text{Green}}
\]