I have tried all three on the same bass. 760 sets for all three.
Copper->Gold->White is correct in brightness.
The original Whites pretty much just sound like a stainless string if you softened the top end and got rid of all string/fret noise. Not as bright as a regular stainless round, but as bright as a lot of nickel strings. These are the most flexible, almost like a 40-95 set.
Gold's have the most low mids and fundamental by quite a bit. They also have a really nice presence in the upper mid and are plenty bright for most styles of music. They are HiFi clear, too. I would say they are about as bright as a just broken in nickel XL. They are the best recording string if you want a solid traditional bass tone to cover a lot styles (except maybe bright slap tones or prog metal (maybe with enough high mid boost and distortion)). They can be burby and growly if you want, but get fat and round when plucked soft near the neck. These also have the highest tension of the three and are not as flexible.
Coppers are more mid focussed and have a bit of natural distortion to their high mids that makes them sound really warm. Their lows are round, but not as full as the Golds. Their highs are also there, nice and extended, just not enough to poke out in a mix. The have a little looser tension than the Gold's.
I used them with series and parallel pickups, p-type grindy neck tones to Matthew Garrison emulating bridge tones. Anything from traditional R&B, country, jazz, soul, folk, rock, and contemporary Christian.
For fretless, you could put the Coppers on and probably never want to try another type of string.
For fretted, I liked the Gold more. The extra highs and clarity just add a little something more. The bit of distortion from the Coppers can also make the grind/growl of the frets not as clear. The Whites are just a little plain. Like McCormick Mayonnaise plain, adds a little flavor to a sandwich but nothing special.