That's an interesting point, where did the maker of the SVG for the Venetian Flag get his purple and cream from, as the part that is purple should be Venetian Blue, whilst the cream and such should be Gold. From my limited work vectorising such badges and flags, generally you'd use what you're working from for the colours. Surely he wouldn't have just used default colours, and even if he did, they'd surely be closer to the actual colours than this was.
That said, even if they were default colours (very odd default colours mind you) for some program, the odds of the creators using that particular default program, and picking, at random, those particular default colours, seems very slim indeed. You're right though, without knowing exactly where these colours on the flag actually came from, there is a very small chance that this is just some very big coincidence.
That said, when you throw in that Riga looks almost certain to be replaced, it would still take close to a miracle of sorts for this all to be some huge coincidence overall.