To get a reasonably accurate spelling, you'd need to consider:
* Which Gaelic? Scottish Gaelic or Irish Gaelic? They're distinct languages.
* Phonetic approach: Transliterating the pronunciation into Gaelic letters. This will give a more approximate spelling.
* Formal vs. informal: There might be slightly different spellings depending on the context.
Therefore, instead of providing a definitive answer, I can offer *possible* transliterations:
Possible Scottish Gaelic Approximations:
* Cailean Donn: This is a likely rendering, using "Cailean" (Kyle) and "Donn" (brown).
Possible Irish Gaelic Approximations:
* Caoimhín Donn: This uses "Caoimhín" (a name sometimes equivalent to Kyle) and "Donn" (brown). Note that "Kyle" doesn't have a direct equivalent in Irish Gaelic, so a similar-sounding name is used.
To get a more precise translation, you would need to consult with a Gaelic speaker or a specialist in Gaelic transliteration. They could offer a spelling that better reflects the nuances of the name's pronunciation and the preferred Gaelic dialect.