What do the colors on the portugal flag mean?
They do not mean anything.
Significant explanations regarding "bravery", "honour", "bloodshed", "courage", "hope" and so forth, were all later creations made by the dictatorship after the 1930's.
The red flag with a green circle in the center were the colours of one Republican revolutionary flag hoisted in the Oporto City Hall in 1891. From 1891 to 1910, red and green flag colours became the symbol of the Republican movement.
If any historical connection, the red can be directly linked to others 19th century movements, as a symbol of one revolutionary and popular statement.