ideas for method...

There will be SIX COLOURS:

•  red
• orange
• yellow
• green
• blue
• purple

The person will be shown a flashcard with a series of NINE DIGITS 
and another with a series of NINE LETTERS
and another with a series of FIVE WORDS

Of course all the flash cards in its type will be the same though the characters shall be printed with different coloured ink.

I will probably set a time limit for the viewing of each flash card.

FIGURES
I will try and get 15 per colour... so that's 90 people altogether.
I CAN DO IT.