There isn't generally a big difference in colour between a gas and a liquid. They're the same stuff, with the same molecular bonds. The main difference is in density, and some second- or third-order bonds that enable the liquid state.

So I'd imagine that a nitrogen lake would look a lot like our nitrogen atmosphere (or it would for the first 10m or so [ the equivalent thickness of the atmosphere, if it were a liquid] - but 10m of water is pretty transparent, too. you need 30-100m before things start looking blue...)

The liquid-solid transition involves much more cross-linking of chemical bonds and crystallinity. Solids are generally opaque while liquids are transparent. Watch max melt, or ice... (but remember we are often seeing the effects of impurities)