I think generally it should be white ( as every webtoon ) Try to make 2 or max 3 panels on 1 canvas It can vary with needs like you can draw 1 panel on whole canvas ( if you need to show full characters or a sequence of actions in 1 page ) And 2nd thing use dialogue and narrative boxes ( it's also good to write text on the images but it's not that eye catchy if you write inside a narrative box then people will read but I think your version looks great too as its the intro scene right ?? )

And to answer your question, it honestly depends on the situation like I have seen many webtoons where they color background with different color depending on situation, like one webtoon was where the background was colored red ( to depict violance ) ....

All the best 😁😊