What gives carts that nasty red color?

Does anyone know what gives some carts that nasty looking dark red/rust color on the connector board PCB ends?

I've mostly seen this with Genesis carts. I have a new game, and an old used copy of the same game, the new games PCB end is off white, and the used one is a dark red, almost a rust color. But it can't rust since the PCB board isn't metal.

Anyone know what this is from? Smokers home?

Believe it or not, there are simply different color PCB's out there. In working with lots of used games, I've seen the same cart have white, red/rusty, or green. It must have something to do with a variety of boards used while manufacturing. MK2 from Acclaim is a prime example, there's millions of those, and I've seen one with every color board.

Yeah, there *are* different colour boards, but I think he means discolouration when you see the actual colour of the board.

Its just dirt of various sources. That edge will absorb anything so it'll stay that colour. Dust, grease, sweat etc. is easily got on there. Don't worry about it!

Isnt that when you enable red blood in the bios ?