blue spots on my screen

Do you have access to an external display that you can plug in? See if the image is clear on the external. If so we know the problem is strictly within the internal display circuitry at that point.

Here is the IFIXIT guide to open up your system to replace the display assembly which is the easiest way to fix this: MacBook Unibody Model A1278 Display Assembly Replacement. But before you do that lets first try reseating the displays data cable. After opening the system as outlines in the first few steps (to Step 5) jump to Step 9. After removing it make sure there is no dust in the connector and reseat it. Power up the system to see if that fixed it. If not its time for a new display.

Replacing the complete assembly is more expensive it is the easier path. Your other option here is to replace only the LCD panel but its a lot more work and you do need to be careful as you can damage/break parts in the process which will either make your system look trashy or cost more in added parts. Here's the IFIXIT guide for the LCD replacement: MacBook Unibody Model A1278 LCD Panel Replacement