Removed headline from first screen by request.
Spelled colour names uppercase raise the challenge. Changed colour set to make the colours better identifiable.
Reduced number of Questions and the duration of the focus mark in the dry run (heuristic).
Reduced duration of focus mark, delay before the tube box is displayed and the time for user input to raise the challenge (heuristic).
Shortened feedback sentence.
Shortened instructions.
The label of the box is no longer constrained to the colours used for the blood tube, but chosen randomly among all colours. This currently favours 'N' to be the right answer, but this issue can be solved ohterwise.