Limestone Fireplace - chips

In September I had a limestone fireplace installed, during the installation process I noticed a couple of 'flaky' patches where the limestone came away leaving a dent.
I asked the fitter and he said that this was normal as limestone is very soft (wish I knew before I bought it) and that he would use a special filler on it.
Anyway to cut a long story short the installer returned today and gave me a bag of special 'sandstone' filler supplied by the fireplace manufacturer. He said that this comes in minute quantities but gave me a huge polythene bag of this special filler,
The bag that he left contains a pure white powder that looks like standard polyfilla - and I can't convince myself that this is correct because when it is mixed and used on the fireplace I have bright white patches on my ivory coloured fireplace. ( I keep thinking he looked at me saw female and decided that he could give me anything)
I have tried contacting the fireplace manufacturers but they don't reply so I don't know who to ask.
Does anyone know anything about Limestone fireplaces? - would you expect it to be chipped before it was installed?
Is there such a thing as a special filler?
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