How to make particles a different color depending on which side they’re on? Ok I have a particle system (in 2.8) where the object emitted is a meatball. I need to have the left side of the emitter emit red metaballs and the right side blue, with blending in the middle. I probably need to use a colorramp here, but don’t know what the exact node setup would be. 

Here’s a diagram of what I need where R is red side and B is blue 



How can I do this?
The color ramp factor can be based on the velocity info of the particle system. Or you can use "Object info" >> "Location" or "Geometry" >> "Position" as an input, but those are based on the world coordinates, so they will work only in the Origo.