Words and concepts – a personal thing?

From Stephen Downs' OLDaily:
http://en.wikipedia.org/wiki/George_Lakoff

When I was a child I learned that there were six colours in the spectrum. I even learned a little rhyme to help me remember. Red and orange, green and blue, shining yellow, purple too, all the colours that we know, live up in the rainbow. Somewhere along the line, someone added a colour: indigo. Ask me today what colour something is and I'll probably use one of the words in my rhyme. Indigo? Never use it, never even see it. Do I need the word for the colour to exist? Do I need to have learned the concept to distinguish indigo objects from others? This short article, unattributed but reading a lot like George Lakoff, suggests that concepts can exist even if the words don't.