I just saw Featurette 2, and I noticed the rather dark purple/blue on a white background for Portugal - which obviously is a sea-faring naval empire. Then I realize that Firaxis' choice of cream and violet for the potential Venice civ is even more fitting. What I refer to is the psychology factor here: 2K have subliminally picked those colours, because Portugal and Venice have a number of things in common, e.g.:
-Mediterranean or near-Mediterranean coastal European nations
-Mid-2nd Millenium AD powers
-Seafarers, naval powers
By picking those colours, Firaxis are more or less saying they are two sides of the same coin.
In short, the colour choice of Portugal strengthen the case of Venice being in for purely psychological reasons, on a subconscious level.