It doesn't sound normal to me...
However, an LCD that does not have 100% even lighting across the entire panel isn't necessarily a defect and could be within the acceptable range. However, very dark areas or discolored areas are not within any acceptable range.
Mac mini (Mid 2011) 2.7 GHz i7, 8GB RAM, Crucial M4 256GB SSD + 500GB + 1TB FW800 OWC Mercury Elite Pro mini
iPhone 4S • iPod nano 8GB • Sound System Audio Engine A2 • Display UltraSharp U2412M 24"