In Irish "oráiste" is only the name of the fruit, not the colour.
"Buí" is the Irish for the colour orange.
As I'm sure you realise, "buí" also means "yellow", in fact Irish speakers divide up the spectrum of visible light differently to English speakers (the seven colours of the rainbow are actually a cultural interpretation and have no basis in physics), so in Irish the word "buí" covers the whole range from yellow through to orange.
If you want to be more specific about a particular hue, you can use "flannbhuí". This is a bit like using terms like "navy blue" or "sky blue" in English.
As well as Peachey's example of terms for "red", another instance of colours not corresponding in the two languages is "glas", which can be translated as "blue", "green" or "grey", depending on the context.