I have been a painting contractor for 13 years and sold paint for 5 years prior.
It's important to clean the siding of all mildew and to remove any oxidation. If there is any bare aluminum, then use the appropriate primer. 100% acrylic paint works well with aluminum as long as you use vinyl/aluminum siding safe colors. Make sure you stay in the shade when applying the paint.
Sherwin Williams has a spectrum of colors that are safe for vinyl and aluminum siding. Kelly Moore and Sherwin Williams are both quality companies that will be able to provide you with everything you need. If you don't like the blank stare or incomplete answer from an employee, ask to speak to someone who actually knows what they are talking about. Don't go in on a Saturday, that is when they usually have the people who don't know anything working.