Though it doesn't look like it, the word 'corcra' is actually related to the English word 'purple'. Way back in time, Old Irish almost entirely lost the letter 'p', with initial letter 'p' disappearing completely and 'p' changing into a 'k' sound, thus you get words like the 'athair', which means 'father' in Irish and 'pater' in Latin, which share a common ancestor, but the word in Irish lacks the 'p'.
Shortly after this happened, Irish came into contact with Latin speakers, and would borrow vocabulary from them, and the Latin word 'purpura' was one of them, but because Irish lacked a 'p', a 'k' sound was substituted, thus leading to 'corcair' and subsequently 'corcra'.
The other lesson to learn from this is that if you see a word starting with 'p' in Irish, it was probably borrowed from another language.
That is an interesting example! This process happened in Gaelic languages of Irish, Scottish and Manx, that is why they are classified in the q-Celtic group, whereas Brythonic (Breton, Welsh and Cornish) are p-Celtic.
E. g. the word "head" is ceann in Irish and Scottish Gaelic, kione in Manx, but penn in Breton and Cornish and pen in Welsh!
Interestingly, the Celtic languages aren't the only IE language family with such a split. A similar split happened amongst the Italic languages, with Latin being one of those that ended up with [k] and some of the others ended up with [p]. Of course, then the Roman Empire happened, and we all know what happened after that. It's particularly interesting, because the Italic family of languages are thought to be the IE branch most closely related to the Celtic languages, and there's even a story that during Caesar's conquest of Gaul, he switched to speaking Greek because he realised he could understand a fair bit of what the Gauls themselves were saying. Apocryphal or not, if you've ever seen Ancient Irish inscriptions, they do bear an uncanny resemblance in some ways to Latin, in that some of the inflections are similar, and some of the words wouldn't look out of place in Old Latin.
In fact, if you want to see an inflectional ending that has remained intact in many of the Romance languages and the Gaelic languages, the ending -(a/e/i)mos (which ended up as -ons in French, and -amo in Italian, and I couldn't tell you what it is in Romanian) and -muid in the Iberian languages and the the Gaelic language for the first person plural present tense are etymologically related!