Am I the only one seeing a clear difference between the two whites posted side by side? I'm not arguing for or against, but I think it's worth pointing out that while the purples are the same, the whites are actually quite different.
The only difference between the colours appears to be artefacts from compression, which is exactly what's to be expected considering that we only have small dots on a compressed image to get that one from. Even so, whilst there is a "visible" difference (which most people would miss), the actual number values of the colours are again pretty much identical.
Put bluntly, the colours of the "unknown" civ are the ones from the Venetian flag, and the only way this could conceivably happen is if they got it from said flag. Now either they thought the colour pairing was absolutely dapper after having spent some took looking at the Venetian flag in detail, and decided "well whatever, let's use these colours off the Venetian flag on someone else why not?", or they decided to use these ones for Venice whilst looking for an appropriate, but unique, colour combination for them.