Let me show how I painted the flag.
I started by dividing in three sections the flag; green red and then white...just drawing a line to see the proportions.
Once done it I painted the base of the three colors, a flag green, a white and a carmine red, all Vallejo colors.
I consider this phase very important....it needs to be really uniformly painted and I spend a lot of time to do it.
Here you can see the red and the white base (white plus beige).
..so, i stared with the green part giving the lights, and highlights adding "Sunny skin tone" and "basic skintone"
the shadows have been given adding at the base a bit of "black" and "carmine red".