If you check out the flat flags the colors are exact, obviously the styled ones have subtle shadowing etc, and are probably out by a very small margin.

I checked out Estonia from above and the colour doesn't match the examples on Wikipedia. I've also checked out the Australian flag, and it's eyeball-different - the blue in the real flag is closer to navy blue. The blue should be #002B7F, but a colour picker tells me that the 64x64 flat flag has a blue of #003399.

It's not a big problem in my opinion - no-one should be overly hung up about minor anomalies like that for web icons - but it's not true to say the colours are exact.