Damaged Fireplace Hearth Tiles - Tile Advice

[Svenedin]

This is my first post on the forum. I'm Stephen and I am definitely not a professional tiler. I can do basic tiling like a few tiles around a basin in a bedroom or replacing a cracked tile in the bathroom. I've also successfully retiled where I had to replace a shower mixer bar but anything else I would call in a professional.

Anyway, this question concerns damaged hearth tiles. I have 3 arched, tiled fireplaces. Probably 1920s but may be earlier (the house was built in 1904). The tiles of the actual fireplaces are almost perfect but quite a few of the hearth tiles are cracked and chipped. Presumably this is from fire irons being dropped. The cracked tiles are not at all loose but the cracks fill with ash and I don't want them to deteriorate further. I think the tiles are set in concrete.

There is very little chance of finding replacement tiles especially as the hearth tiles match the fireplace. I wonder how I can fill the cracks without it looking awful? Whatever I do has to withstand great heat. I am considering using a cement based grout and a cement dye to get a reasonable colour match and using that to "grout" (fill) the cracks. Would this work?

Pictures show cracked tile and the 3 fireplaces. 1 is back in use, the other 2 are works in progress.