This story is likely from a children’s anthology. Little boy lives in a spaceship (maybe space colony?). He has a pet (maybe turtle?). Pets are rare due to scarcity. A group of visitors come (maybe from another colony) and are amused by the pet. The boy is pressured to give the pet as a gift to the visitors.
The book I’m looking for is a picture book from my childhood. It’s about a small green creature, probably a lizard, who is looking for a home. He might also be trying to get out of the rain. He winds up finding a mushroom to hide under. The mushroom top falls off the stem and lands on his back, making him a turtle. The style of the book is very 1970s, though I’m not sure when it was published. The mushrooms in the book are tall and red with white spots. I also remember a yellow mushroom in the book with the same style.
I have included a bad drawing of how I remember the turtle looking by the end of the story. The mushroom might have been larger than in this drawing.