Murky, orange coolant

I just removed the water pump in my 2010 GTI (Original pump, no issues at all with it, just figured I'd replace it since I had the intake manifold off anyway.)

I've had the car since new and performed regular coolant flushes on it every few years or so. Last one was 16 months ago at a VW indie specialist - receipt says Coolant Flush and Fill G12. I've never seen the level drop in the overflow tank, and the coolant in the tank has always been a nice, clear pink. Never had any overheating or warning lights or any issues.

So, I was kind of surprised when I pulled the pump and murky, orange coolant started gushing out from the hoses and the head. Yet the coolant that came out from the oil cooler side of the pump was clear and pink, like the stuff in the tank. I get it that maybe rust in the block would discolour the coolant, but why wouldn't it discolour all the coolant?

How can half the coolant be clear and pink while the rest is murky and orange? Can there be two totally separate circuits for the coolant? Could there be a valve somewhere in the system that's stuck and not letting the coolant circulate completely?

I guess I'll try to flush it completely and start over with fresh G12, but I'm worried there might be some other issue. I'm also wondering if that indie shop actually did the coolant flush they charged me for. Seems odd that the coolant would look that bad after only a year and 20,000 km. Thoughts?

Well, guess you learn something new every day...

So, I had a chance to get back to the car today. Pulled the drain pan from under the car and it was filled with murky orange liquid. Poured it into a clear plastic jug and... magically it’s now clear and pink!

So I guess when you look at the coolant against the background of a black hose or the inside of the block (or a black drain pan) it looks orange and cloudy. Same coolant on a bright background looks clear and pink. I had no idea.