Step 1: Compare frequencies:
Using $E = h\nu$, the lowest energy means the lowest frequency.
Approximate frequencies: violet $7.5 \times 10^{14}$ Hz, blue $6.5 \times 10^{14}$ Hz, yellow $5.2 \times 10^{14}$ Hz, red $4.3 \times 10^{14}$ Hz.
Step 2: Conclusion:
Red has the smallest frequency in the list, so it has the smallest photon energy. Violet is the opposite end and has the largest energy, so A, B and C are all more energetic than red.
Final Answer:
The lowest energy colour is red, option (D).
\[ \boxed{\text{Red}} \]