One of the main items on a MacBook Pro to go out after water damage is the keyboard and keyboard connector. If you have already replaced the entire top-case, that would lead me to believe it is the keyboard connector that is damaged, blown, or corroded still. This would need a new Logic Board, or at the very least a component level repair. Of course you could also use an external keyboard as well.
Is the fan the only thing that is not working? After opening up the back, you should check the fan connections for any corrosion and clean those off as well as any other connections inside the computer. If those are all clean you can also do an SMC and PRAM reset that may help. SMC Reset: Shut down the computer. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time. Release all the keys and the power button at the same time. PRAM Reset: Immediately press and hold the Option-Command-P-R keys. You must press this key combination before the gray screen appears. Continue holding the keys down until your Mac restarts, and you hear the startup sound for the second time, and on the third chime, release the keys.
Flickering pink background is caused by failing graphics chipset in the Logic Board. Most likely, the logic board will need component level repair to get back to normal. I wish it was as simple as a display replacement.