Green Brake Fluid?

Recently replaced the front brake pads and rotors, (will be attempting the rear drum brakes soon). I also did a brake fluid flush by removing the old fluid from the reservoir and doing the brake pump method to push the old fluid out through each bleeder (front and rear, farthest from the reservoir to the closest). I made sure to not let the level fall below the minimum during the flush.
I was a little concerned that the old fluid was green and the new fluid was a clear light yellow...

I used Toyota OEM DOT3 brake fluid.

Plus side though, my ABS light turned off after the flush and hasn't turned back on (~300 miles since the flush.)

 

I’ve had a Toyota tech tell me it was the breakdown of grease in the master cylinder. Others here on the forum mention it’s from the water in the brake fluid reacting with the copper in the lines. I don’t know who’s correct, but it just points out that it needed to be changed 10s of thousands of miles ago I guess?

 

Brake fluid looks visually green when old. I always heard it was due to copper content.

 

I guess the green would make sense to be copper, I will probably do another brake flush in ~5000 miles or so to try and flush more of that out. I haven't had any issues with braking. I did notice an improvement after the front brake and rotor replacement & flush, but just the normal improvement after putting on new brake pads. I'll keep an eye out for leaks, but I guess better late than never

 

It usually takes on tinges of increasing greenness for me within weeks of flushing. It’s normal. Brake fluid is hygroscopic, meaning it absorbs water, which is why steel brake lines can rust from inside out, and where precipitate (/contamination) that gums up caliper pistons can come from.

I took a min to dig b/c I was curious. The gist I got is this: The fluid is light clear-yellow. What happens if you mix dark contaminant into clear yellow? It looks increasingly green, until it’s black enough you can’t see thru it.

I also saw a lot about copper, that fluid test strips and meters flag based on copper content (not sure that’s true though), water in the fluid binds with copper to oxidize it making copper oxide which is green, but I don’t think copper is reactive enough to get hydrogen to break its bond with copper or copper plumbing pipes would make zero sense!

It’s interesting for sure, I think “contamination” I’d the correct answer.