The biggest question here is why is it green. Learn how to get the Pickhammer in My Time at Sandrock.
The plot around My Time At Sandrock revolves around you becoming a stellar builder. But, as it turns out, you'll have to work a double shift as a blacksmith to upgrade your tools, too. To complete the main quest The Show Must Go On, the town's stage must be fixed. If you don't, the city won't be able to say their goodbyes to the builder you're substituting: Mason.
1x Sharpening Stone: purchased at Hammer Time for 512 gold. Related: How to upgrade your Workshop in My Time at Sandrock All the machines mentioned above can be crafted at the Assembly Station in the workshop. Though it takes a lot of work to build a Furnace, a Recycler, and a Grinder, you'll need them to be good at your builder job. I'd recommend keeping two of each when you get the time and resources to make the crafting process faster.