What Sean said.
The problem is that with very light colours, you see every variation in coverage. Trying to build up the coat in multiple layers is likely to only get you crazy.
I airbrushed my Iyanden Yellow on white primer.
http://2.bp.blogspot.com/-NoHLwmUfDgo/U0E9gtsskcI/AAAAAAAAAxI/T0kku6nViz4/s1600/Eldar_Army_20140406_131007.jpg
What is not done in this picture is adding shadows by painting over the bright yellow with a more muted yellow/orange.
I'd follow Sean's advice and get either a generic spray from the home improvement store that matches your base yellow, or try to find an army painter or equivalent primer in the right colour. Natrually, with a product that is made for our use, your experimenting need is reduced, but the cost per can is most likely higher.
Maybe Army Painter Colour Primer "Demonic Yellow" is the ticket:
http://shop.thearmypainter.com/products.php?ProductGroupId=2