It's not bad looking, but that's all a matter of personal taste. You could try a stone enhancer on a scrap piece to see if it brings out the color. As far as the grout goes, you will have to do something as the patch really stands out. Re-grouting is very time consuming as the existing grout has to be ground out first. There are many other choices, from river rock and cultured stone, to a more formal look like polished marble or granite tiles.

My opinion would be to stick with the character of the rest of your house. If you have Coastal and Craftsman features, don't go too Contemporary or Formal. Both examples that you have posted. ;) Besides the siding on the outside of your home, do you have any hard surfaces, like brick or stone? If so, match those instead of bringing in a third element. We recently built an outdoor area for our home. I had my heart set on a stone fireplace, but the house is brick and stucco with a wooden screened porch. The more that I thought about it, the more I decided that bringing in another element was too much. Matching brick would be the way to go. I am so happy with my choice. We also have columns that mirror the columns on the inside of the house and painted to match the screened porch trim and stucco accents. A cedar wood pergola is stained to match the darker taupe of the majority of the stucco. All colors blend in with the brick. If your house is all siding, then I would go with the stone. for inside and out. I believe that the plaster both outside and in, as shown in photos 2 and 3, would be too contemporary and formal for your home. I like the interior stone and wood trim photo that you posted with the hearth, but sadly, you do not have room for that set up. Another opinion...I'd take down the knee walls. You don't need them for a division. The one between the window is taking up valuable wall space. You can create a natural division between the dining and living space with your furniture. I know from experience. We put a built-in in our living room, and I wanted it to have some character, so the middle section sticks out about 10 inches beyond to side sections. That middle section has become a thorn in my side and prevented a couple of different seating configurations that I would have much preferred in that room. The bump-out gets in the way. I think that your knee walls will narrow your walking space, getting around furniture, such as a sofa. Again, just my opinion.

Natalie Myers just redid her fireplace grout to look more- well i want to say modern, but it’s actually more of an ancient look. you add more grout in between so it’s more of a flat finish with wide light grout. Here’s a link to her blog (its saysdays gone wrong but it’s because she tried to DIY and ended up hiring someone to do it for her. This could be cool combined with a light limewash too. https://www.veneerdesigns.com/post/an-overgrouted-stone-fireplace-diy-gone-wrong

Paint does wonders. There is also rambio limewash. Looks like paint but it allows the bricks to breathe I guess. Ive heard great things and plan on using it dor exterior brick. for my fireplace I primed the brick first with two coats of Kilz and then one coat of paint. such a huge difference it made. Our moms thought we were crazy to paint the brick. Now they are in awe and cant believe the transformation it made.