Turns out that there are practical reasons behind the sartorial choice. Zuckerberg has said the shirt is his typical daily uniform because it helps him limit the number of small decisions he has to make in the morning.

It also turns out that Zuckerberg’s shirts are not just any plain gray t-shirts. You might be surprised to learn that they are custom made and sourced from a well-known Italian designer. Each shirt costs between $300 and $400, and they aren’t available for the public to buy.

But a 26-year-old Austrian fashion entrepreneur is looking to change that. Klaus Buchroithner, who also owns the clothing company Vresh, is making “replicas” of Zuckerberg’s standard gray shirt. His Zuckerberg Shirt, which costs 40 Euro (about $47), ships to residents of the United States and the European Union. Buchroithner says all proceeds go to the Chan Zuckerberg Initiative, an organization set up by Zuckerberg and his wife, Priscilla Chan, to work on causes from health to education.

We talked to Buchroithner over email to learn more about his Zuckerberg Shirt. Here’s what he had to say. This interview was lightly edited for length and clarity.

Fortune: When and why did you start the Zuckerberg Shirt project?

Klaus Buchroithner: When I read Mark Zuckerberg’s post on Facebook about everyday decisions like what to wear and his solution of a wardrobe full of grey shirts, I was quite impressed by the simplicity. It made me think, “Ok, what would I wear if I did wear the same shirt every day?”

Since Mark probably put a lot of thought into it, I started to research which specific shirt Mark picked for himself. This led me to Brunello Cucinelli, who is an amazing fashion designer from Italy with a great hand for fabrics. Unfortunately, you can’t buy Mark’s shirts in Brunello’s store. So I decided to design and produce a replica that is as close to the original as possible.

I’ve been producing fashion all my life. I always try to create something unique and special that people love, with great quality, sustainable and fair. So I produced a few examples to get a feeling for what would make a great replica. I was quite satisfied with the results, so I wanted to make the shirt available to everyone else who is interested. With the shirt I also want to bring more attention to the Chan Zuckerberg Initiative.

How are sales going? Is there a team with you behind this project?

KB: I have gotten orders from all around the world. It’s a huge honor for me to see that so many people are interested in this project.

The fabric is from Italy and I work together with a small factory in the North of Portugal. I know the people there and I am happy working with them.

Does this project have anything to do with your other company, Vresh?

KB: No, this is a new project, but I do use the same contacts to organize the production. Vresh is a Boardsport brand, focused on high quality clothes made in the EU. The V is for Value and that means that everyone involved should benefit from the brand. We make sure workers receive a fair and sustainable compensation. Our customers are able to buy a fair produced high quality product at an affordable price. This is possible because we focus on direct sales and also the environmental benefits from the long lasting quality.

Your website says that 100% of the Zuckerberg Shirt proceeds will go to the Chan Zuckerberg Initiative. Why?

KB: Their work in research, education and technology is very important and makes a real difference. That’s why I am donating all profits from the shirt sales to the initiative. HIV, malaria, and cancer are terrible diseases that humanity still cannot manage. Thousands of people worldwide are starving every year or die from untreated diseases. Only with better technologies and education it will be possible to handle these issues. If people like Zuckerberg bring such initiatives into life to cure incurable diseases or to revise education, there is no alternative for me.

Was there some special importance to you that these items are handmade in the EU?

KB: Many big brands are producing under bad working conditions in Asia. That’s not the way I want to do business. So I decided to only work with companies that treat their workforce well, and what is more, provide a nice product quality.

Any thoughts on the state of the EU?

KB: The EU is in a critical phase now. In my opinion we can only get something done if we work together. I am a bit worried how the EU will work after the Brexit, but the EU is still strong enough to go through all these problems. It would need leaders working together on all the challenges like the refugee crises.

What do you think of gray — and what is your favorite color?

KB: Honestly blue is my favorite color, but as far as t-shirts are concerned I like gray and white most. It is very simple to dress with these colors and combine with different clothes.

What do you hope your customers gain from the Zuckerberg Shirt?

KB: I hope that my project brings more attention to the Chan Zuckerberg Initiative and their projects about science, education and technology. What is more, I hope that my customers have to think a bit less about what to wear in the morning and a bit more about how to make the world a better place.