MacBook Pro (17-inch, Mid 2010) screen displaying low number of colors

The fact that it boots perfectly fine in safe mode points to a problem with your graphics card. Safe mode disables all hardware drivers besides those absolutely essential to the operation of your system, and that includes hardware graphics rendering. The reason your graphics are so choppy in safe mode is because everything is rendered in software (i.e. by your CPU) rather than in hardware (by your GPU). I doubt it's a hard drive issue simply because you have no problem installing ML or booting up.

The good news? Since your repair was around a year ago, you might be able to convince the Apple Store people (talk to the manager) to replace your logic board for free.

Typically Apple will replace (instead of repair) a computer that has required 3 repairs for the same issue.

It may require a call to Apple Care (800-273-2273) and ask to have the case escalated. If you have taken it to the store already, and the store has refused to replace, then Apple Care will probably back the store's decision. If however you call Apple Care first, and when they say to take it to the Apple Store for repair, you question the need for 3 repairs on the same computer for the same reason, ask to have it escalated, you will probably get offered a replacement.

If that gets you nowhere, You may also try a EECB (Executive Email Carpet Bomb) to various service level contacts. sjobs@apple used to get results, may try tcook@apple.com now? Or do google/consumerist search for EECB and Apple. http://consumerist.com/2007/05/11/how-to-launch-an-executive-email-carpet-bomb/