It makes sense that a white flag should represent Zero since this is considered all colours. White is a unique colour since its specturm has all the colours.
Additionally the stars in the canton area can be substituted for another icon, so long as the pattern matches.
This system of flags departs from the international maritime flag system which is effective yet difficult to remember and understand. The clarity of this the Metric Number Flags is further enhanced by the colour of the stars.
The flag for Zero is a black star on a field of white.
The flag for One has a white star on a field of red.
The flag for Two has a black star on a field of orange.
The flag for Three has a blue star on a field of yellow.
The flag for Four has a yellow star on a field of green.
The flag for Five has a red star on a field of blue.
The flag for Six has a white star on a field of indigo.
The flag for Seven has yellow star on a field of violet.
The flag for Eight has a white star on a field of black.
The flag for Nine has a blue star on a field of pink.