I didn't pick this one, but I'm pretty sure it's a mouse-pee pinkgill (Entoloma incanum). (No, I'm not tempted to eat anything named mouse-pee.) It's the greenest 'shroom I've ever seen, though.
Here's a spore print, helpful in identifying mushrooms. You just remove the stem and lay the cap gills-down on colored paper for a few hours.
Below, Richard checks out a big one. And bottom, he found a hollow stump with cascades of these lovely little sticky golden ones growing inside.