Learn English – Shall I use ‘in’ or ‘on’ or ‘during the course’

All three could be grammatically correct in colloquial English depending on the context. Here are some examples, though not exclusive:

1. The pool looked gorgeous in the night, but in the morning we saw trash at the bottom.

2. The pool looked gorgeous at night. [This is fine as is, and is the most likely usage.]

3. The pool looked gorgeous during the night, while lit by the floodlights.

Example 1 implies it might not always look good, and 3 implies a duration. English is flexible, and in this case, there is no intrinsically wrong answer.

I suggest you to use "on" because when we are watching something on screen, using "on" is more appropriate.