Much of the difficulty in diagnosing colour defective vision is in the way testing is carried out. The most popular method, the Ishihara plate test, is commonly known to people as a series of cards with apparently random coloured dots on them within which numbers can be made out by those with non-defective colour vision. Now almost 100 years old, this test is fallible and time-consuming but the best we have. And the reason for that...is language.
The only way that we can tell the existence of colour vision defectiveness without Ishihara plate testing is when colours are named... and that's when confusion arises. After all colour is subective. One person's beige is another one's brown. The names we give colours, outside of the primary ones, tend to relate to objects. Lavender, pillar-box red, midnight blue, emerald green. Even more fun can be had with paint charts where an army of people come up with names that make the mulberry burst and keep the moroccan flame lit. The imagination creates the mood.