If you search the archives, you'll find the answers to all your questions with text and illustrations.
Without affirming the year, and including photos, you'll illicit little help.
If you have a 1967
, only a 1967
black tank will work as a direct replacement, they are interchangeable, but not identical. 1966
or 1969 tank has ZERO similarity to '67/'68.
The plastics in 1967
rear baths, in all length trailers, except caravel
, have many interchangeable parts. They may have been offered in blue, green, pink, beige, or yellow. It's hard to say, but the best clue to color theme is kitchen appliance and counter-top color.
In my all original 1968
bath, I have four colors, which are dependent on the state of fade and oxidation of the different plastics; Fiberglass, Melamine, PVC, ABS...
Again, Pictures of what you have encountered, and are trying to solve, would help forum members assist you to a greater degree. Someone can answer you with great specificity, if you know what you have, or show pictures.
If it's a 1967, its is a great year to restore.