Chrysler did not offer a Tropical Turquoise in 1962, but did offer a Bermuda Turquoise. So, the seller is wrong on that point.
There is no Dodge equivalent to this colour - it is a Chrysler-only shade.
As with virtually all colours, shades changed from year to year. If a colour was popular it was carried over to the next, and in some instance when a colour was less popular than planned, and the factory had lots left over, the colour will be carried forward to use it up.
As to lighter and darker, there is no rhyme nor reason. Just depends on what was considered popular.
In 1966 Dodge had one turquoise shade - Dark Turquoise Metallic, code L. In 1965 Dodge had three turquoise colours, light, medium and dark, plus a Spring only shade, Pale Medium Turquoise Metallic. Obviouly turquoise shades were not as popular in 1965 as Chrysler thought and the choice was cut back for 1966.
If you want to know if a colour is carried over from year to year, take note of the Ditzler, DuPont, CIL, etc. code. The code used on the car (A, B, C, etc.) may change from year to year even if the colour does not, but the paint manufacturers' codes do not. If the colour is the same, the paint company code remains the same, even a decade later.