It's not uncommon to see white or even rust colored stains on a freshly sealed asphalt driveway or parking lot. The natural inclination would be to blame it on the sealer, but the stains actually come from natural compounds found in water, gravel and soil.
Mineral Salts can dry on the surface as a result of water run-off. They can also be pumped up through soil and gravel to the asphalt surface. White residue will often show up where there are cracks.
Calcium Carbonate is also common in soil and gravel and can leave a white residue.
Rusty red orange and brown are other common colors of residue left from rusty cars and plant byproducts.
Stains are more noticeable on freshly sealed asphalt, due to the contrast. Be patient, the stains can't be avoided and will wash away in time.
Investigative Geology Report http://www.nacsupply.com/documents/AsphaltReport.pdf