Being Amphibious they’d be close to both coasts and the water.
I actually imagine their home-world being larger than Earth, oceanic, but covered with small islands and archipelagos. It’s in the Human ‘goldiocks zone’ in it’s system, so it’s otherwise the same (Character note: And also how a Human oceanographer would end up wanting to um…be with a Gregorian, in the first place lol.). It simply orbits a slighty hotter/bigger class G star.
With that in mind they’d spend most of their water time, closer to the surface, and anyone who goes swimming knows the sea has it’s own colour changes based on light, as well as depth. Mix that in with the ability to see a changing sky, they’d start to associate the said colours/shades as time. (Side note: Pressure and temperature changes would then start to equate to distance units.)
In their chants-speech, this is expressed by a slightly faster rhythm during the ‘day’, and a slower one during the ‘night’.
Wow, I could go on. But I won’t bore you any further today.