My advice is to do a very pale grey undercoat. It costs no more...just ask your supplier to tint the undercoat. You will need to do 2 coats of your new colour. That is best practice, don't forget to sugar soap and rinse before painting.
When we were getting our home ready for sale we had to paint over an exuberant teenagers royal blue and red paint job. 3 coats of "cream" ( I can't remember the colour name) paint did the job.
