As you head into Wales, perhaps going on holiday or perhaps not, you happen to glance to your right while driving down the the M4, and you see a sign for Castell Coch. To be fair you can also see Castell coch if you happen to look at the right time.
And you wonder what Castell Coch means?
If only you had learned your Welsh colours, you would already know that Coch is the Welsh word for red.
If you want more colour practise, have a look at food and drink;)
Mae'n las 'it is blue'is an example of a soft mutation. Glas 'blue' has become las.
See also Welsh phrases.