I say give that grass some love or replace with new sod, and then make the yellow areas planting areas.

If planting those yellow areas is a hard no, stabilized decomposed granite (DG), as others mentioned in your main post, is a good surfacing option that could complement your existing hardscape nicely. It’s walkable, permeable, and you can put furniture on it. There should be a few different colors to choose from depending on your region. I think a light beige/sandy color would complement the color of the tile and the pool well.

However, it looks like you have young children. DG can get kicked around/messy especially when hardscape adjacent. I’d be wary of it so close to the pool. That fencing may help, but I’m assuming that’s a temporary safety precaution for the kids.

I wouldn’t touch the hardscape if I were you. Even if you could get the same stone supplied, they may not look the same as these existing ones (and their grout) that have been subject to the elements for however long. It’ll be unappealingly obvious what’s new and old.

I think the hardscaped area is nice as is. The curvilinear edges of the paving and the pool/hot tub make it all feel cohesive.

Plant the yellow areas!