The mortar will age in, and be close to a match, eventually. The brick is not a match either. I would buy brick stain as close as you can get it for the mismatched brick, and using a sponge try to get it to match better, or just leave it alone. They actually did a decent job, and its probably impossible to match the brick 100 percent.

Thanks Cat_Ky. I never noticed the brick to be different from the original. The mortar color difference seems to be more pronounced. Unfortunately, I don’t think the mortar will change too much since it’s looked like that for the 20 years we’ve lived here. We were so busy raising our family that I just used a trellis to cover up the area but now I’d like to adjust if possible.

you could use a bit of concrete stain, to match it in if it bothers you that much. Just make sure you get as close a match as you can, because, it could bother you even more, if you get it the wrong color. It also could be, the trellis has protected it so much, that it hasnt had time to weather itself.

It looks like they either used white mortar or mixed their own using white (instead of grey) portland or used too much lime. You could buy type M mortar,add enough water to allow application with stiff brush,let the sample dry and check color match with old mortar. If color is too dark,mix another sample adding 1 part lime to 10 parts mortar for a lighter color.

Adjust % of lime until color matches then carfully apply as thick slury that can be brushed onto grout lines. You can also buy concrete tint in various colors buy I doubt that will be necessary.

I agree with cat. Staining the brick to match is your only option.

I’ve never stained brick, but it sounds like great advice.

I think a window planter on your kitchen window would look nice:

I've seen brick staining done on the TV shows on either 'This Old House' or 'Ask This Old House', and on the TV show 'Restored'.

For the DIYer:

https://www.amazon.com/Brick-Staining-Brickman-Stain-Kit/dp/B01EKCCD26/ref=sr_1_3?hvadid=580671219260&hvdev=c&hvlocphy=9016116&hvnetw=g&hvqmt=e&hvrand=12646692272545156980&hvtargid=kwd-500082252394&hydadcr=8464_13498090&keywords=brick+staining+colorant+kit&qid=1683557667&sr=8-3

The double hung window was done by a real mason. The brick was toothed in, and it appears the mortar joints had to be a bit wider to allow the new infill brick to fit within the existing dimensions of the infill (probably slightly longer/shorter bricks, and didn't want to cut any bricks). So the brick looks pretty good and matches well, but the wider vertical joints distract a bit. The mortar color doesn't look that far off in the pic, but you can try a mortar stain and experiment if you wish.

The casement Kitchen window was done by a beginner fool, not a mason. It was not toothed in and the vertical joints don't even align. The brick, which is a common color and texture, may/may not have originally matched but it looks like it has a white haze which means it was never acid cleaned after installation. It would be too late after 20 years to clean it up. You can try a stain where artistic ability is key, and maybe have to reapply every handful of years. Practice on the mortar match here before going to the double hung window.

Also can't tell from the pic but hopefully that is not a return vent grille for some sort of exhaust next to the window.