Macbook late-2009 not displaying red color
Let me summarize the troubleshooting steps.

Before disassembling:

1- Run the Apple Hardware test to see if it comes up with anything.

2- As far I know you have a NVIDIA graphics car. Run without it to test.

3- Connect a external monitor to test if the internal display is failing.

4- Open up the computer and unplug/plug the Video cable few times to clean the contacts. Or replace the Cable following the instructions here.