I'm not sure about this. I'm making packs of dominoes where the numbers are in their written form as well as another kind of domino which have the colours in written form. For what I call 'Number Dominoes', I've been given 'Dúradáin Uimhrithe', but looking at that again, I have the feeling that this would mean 'numbered dominoes' so I was thinking that using the genitive would perhaps be more appropriate - 'Dúradáin na nUimhreacha'. Similarly, doesn't 'Dúradáin Daite' simply mean 'coloured dominoes,' so wouldn't it be better to call them 'Dúradáin na nDathanna' ?

Oui effectivement - tá an ceart agat

no need of a hyphen when there's a capital letter:
na n-uimhreach(a) vs. na nUimhreach(a).

the capital letter shows that the n is prefixed and isn't a part of the word, to the hyphen isn't needed (in Irish -- in Scottish Gaelic you always retain the hyphens, as in pre-reform Irish)

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne