Here's how they explain it. Even though you're only concerned with naming a word's colour, it seems impossible to ignore the word's meaning. You've just experienced interference . When you look at one of the words, you see both its colour and its meaning . If those two pieces of evidence are in conflict, you have to make a choice.
Interference is the result of having to choose against a stronger type of evidence.
In this case, you have to choose against word meaning, which experience has taught you is usually more important than ink colour.