'Please advise that you need the color collection or swatches for each color.' This isn't correct, you could write: 'please be advised that you need...' which would be polite. If you write only 'please advise' then you are asking that person for their advice to you. 'Do you need the color collection or swatches for each color?' This is ok if you already know the person well. Otherwise 'please let me know if you require the...' would be better.

Hi Yi Wen, It's ok to ask questions in business letters or e-mails. In order to be more polite you could use indirect questions like for example: "Could you please let me know if you need.....?"