Is that the origin of the top quarter of a Greek flag?
Could be:
Papaflessas used an older byzantine pattern for his flag.
Officially the Greek flag was created in thew National Assembly of 1822 as blue and white Cross.This design was not generalised during the GWI but only after the king Otto's arrival in Greece.
Quite by coincidence Bavarian flag and Greek flag was blue and white. So, the Bavarians changed the hue of the flag to much their own.
Officially till 1973 GREECE had 2 versions of flag. One for land (and as from 1923 for Air) use which was a blue field with the Greek white Cross and one for the sea/naval use upper left canton white Cross on blue field and the rest blue/with stripes.
After 1973 all flags are of the naval design. Army still uses as war flags the older design, as many associations like the Scouts organisation etc.
What is the colour of the flag? Varied through the time, as well as crests and insignia differed according to the political status.
while Greece was a kingdom there is a crown, when a republic none etc. Good Information from sites like Flags of the World etc.