We had a bunch of different candies on the table at game night and I gave my friend some M&Ms, he thought they came from a bag of mint flavored M&Ms. He said, "wow I never tried these before, they really taste like mint." We all did a double take, he definitely did not eat mint M&Ms, I don't really remember if we even had mint M&Ms at the table. I believe him when he says he says he tasted mint though, like his brain placeboed the mint into place.
With the grass example, I'm actually not entirely sure! I mean, I obviously know that green is the correct answer, but that knowledge kind of makes me feel like I'm seeing green.
But colour blindness is kind of weird, because for any given thing/colour it's never just "I don't know" - I can narrow it down to a few options, and usually one of them is the correct one; like for a desaturated green, I might think it's grey, green or pink.
I'm colour blind, and if a picture is in black and white, I can't always tell.
A long while back our CRT TV broke, and started displaying everything without colour - I had no idea until my wife pointed it out! It's like my mind just makes up what it doesn't see.
Another example that I always use is grass: if you showed me a cropped image of grass and I didn't know it was grass, I'll tell you "I don't know what colour it is, but I think it's either red, brown or green". But if you point to some grass, I'll always say "it's green!".