What are your color settings in Illustrator? and what ICC Profile is assigned to the document?
If, for instance, you are using Adobe RGB, PNGs get exported without an ICC profile (untagged), so are assumed (by PNG specifications) to be sRGB by anything you view it in that is not color managed: This would cause the difference you see viewing it in Preview.
You can however, embed a different profile with JPG export, checking the ICC Pofile box (
making sure the "Convert to sRGB" button is unchecked in the pulldown)
You could use a certain ICC profile for your Document Color Profile in Illustrator.
Because Illustrator uses that profile when exporting to png, but does not embed it, you must assign that profile later in an application like Photoshop or Apple Preview.