Posting this so my dumb ass doesn't forget how to do it. 
Always back your stuff up before playing around, just to be safe.
Open ppu viewer in FCEUX, write down the values you see for the palette you wanna change.
Open the hex editor, make sure View is set to "Rom File". Click the "Find..." option under Edit. Type the last three values of the palette (if for example it's 0F21313A, you search for 21313A) and click Find Next.
If search yields no results, trying searching for the middle two values (in this case you'd type in 2131). Had to do this in order to edit the clipboard's colors in Dr. Mario.
If palette hacking an FDS game, open game with HxD instead of FCEUX's built in hex editor to make your changes. Found this out while messing around with Galaxian.
You might see more than one instance of the palette, it's cool just play around with them one change at a time and have fun with it.
Color chart! Never use BLACK 0D or else demons (also screen burn)
- nes-color-palette2.png (5.09 KiB) Viewed 89 times