Raw milk mystery

I may have discovered something very strange about milk or tea. Or possibly both.
I've always bought full-cream milk. Nothing fancy. I pour it into my tea and, as you would expect, the tea immediately becomes lighter.
Recently, however, I spotted some raw milk.
It was considerably more expensive, but curiosity got the better of me. I thought I'd give it a try.
When I got it home, I took one sip and was transported straight back to my school days, when every morning we were given a third of a pint of milk. You know the ones.
Little glass bottles of milk, usually left outside in the sun, waiting patiently to become a biological experiment.
But somehow, back then, that milk tasted wonderful, and the raw milk brought it all back. It was creamy, rich and had that proper milk taste I remembered.
Then I poured some into my tea, and that's when things got weird. Normally, adding milk turns my tea a lovely lighter brown, but not this stuff.
I poured in some raw milk. Nothing. The tea remained dark, so I added more. Still dark. A little more. Still dark.
By then, I was standing in the kitchen, pouring expensive milk into a cup of tea that was starting to look as though it had been brewed in a coal mine. I had created what looked like industrial-strength tea.
I have no idea why raw milk doesn't lighten it the way ordinary full-cream milk does. Perhaps there's some perfectly sensible scientific explanation. Or perhaps the tea simply refused to surrender. Either way, the tea tastes fantastic, stronger.
I discovered that if you spend enough money on milk, you can apparently end up with a cup of tea that could probably remove wallpaper.