We have white designed tiles that have a black coloured grout that separates them. However, in certain areas, the grout is deteriorating and cracking. As far as I knew, there was only the concrete/grey type of grout you can use. Can you buy black coloured grout?
After we apply this, is there some sealant we can purchase and apply so that the grout can last longer in the future?
There are all kinds of colors available. I would personally recommend a product called Quartzlock from StarQuartz. It does come in black and it's basically a quartz crystal in an acrylic resin so once it's cured it's nearly impervious to staining. It also has the advantage of being able to go right over other grouts so long as there is enough depth in the joint to accomodate it.