Hi, I have an a700 and have loaned it to a friend of mine who was teaching english in Tunisia. She has been using a Sigma 70-300 and has noticed a great deal of blue fringing on her photos. She also gets a lot of red fringing when using the sony 70-300 but non on the sony 18-250. All the photos are taken in bright light and the Sigma is especially grainy. I can only hazard a guess that she may need to invest in better lenses. She also uses CS3. Any information would be greatly appreciated, Thanks.

She can fix that issue if she's taking the shots in RAW format, opening them in Photoshop's ACR (Adobe Camera Raw).
On the ACR panel, in the right hand side just below the histogram there are tiny buttons. The 6th is the Lens Correction where you can find Chromatic aberration. Just slide the arrows to the left or right while previewing at 100-200%.