There is really no best lighting for an aquarium. It  really depends on your budget and how much you want to spend on  a lighting system. In addition to seeing the color of the goldfish, you have to keep in mind whether or not you intend to grow real plants.  A lot of people like to keep lighting that has a  color temperature range around 6500k, which is a white light similar to what you'd see during the daytime outside at noon.  A color temperature around 2500k will give a yellowish tint and make the colors look softer and more dull.  Whatever lighting you use, pick a bulb with a color temperature range around 6500k if you like that daytime look, which should also display the  bright colors of your goldfish well.

You really only need UVA lighting for freshwater fish aquariums. UVA is the the visible wavelength of light while UVB light is invisible to the human eye.  UVB is used mainly if you have pet like aquatic turtles and reptiles  that bask in the UVB light to help them synthesize vitamin D3.

The lighting you have now should work just fine for both fish and plants.

I have an awesome light that promotes plant growth, and it also shows the colors of the goldfish perfectly! They're glowing red and white It's a tropical bulb by Arcadia. You could take a look in the pet shops if they have them around there! Mine are pretty huge, and I need two of them, so they cost about 20€ each.

Of course! But I don't think you need to worry about goldies losing their color, it's usually happening when they're white at first but with some colored spots. Or black goldfish can start turning red after a few years, which is pretty common among other varieties but moors. So most goldies with black spots may end up all red or whichever the bottom color may be

My Berry is moving her red spots around though (I'd guess she's between 2-3 years old)! At first the headgrowth almost lost it's color, but it's back to be raspberry red again And the spots are also developing farther down to her belly now
Some of my calico fish are also getting smaller white spaces, and aside from that, I only have one colored fish The pearl scales are still too young to tell whether the colors will stick or go.

Now, the old-man fantail in the 20gal is more than ten years old, he was originally a golden red, and has turned a slight bit paler through the years, but that's acceptable due to age. The tancho fantail who lives with him is completely white with only a red circle on the head, which has actually spread a bit more down to the eyes! He's still pretty young, but that coloration usually stays

Lighting on the other hand will pronounce the fishes' colors if you choose the right one! The one I have happens to be a type that makes reds and blues very strong So the calicos certainly look like they have blue skin
And since you probably saw the thread about the yellow ryukin, he had been eating only algae for a long time, so he lost his color temporarily. I'd say the way the fishes' colors react is highly genetical and depends more on their genes than which diet they're fed, at least when considering a permanent outcome

Oh yeah that yellow ryukin was so pretty!

I have 1 shubunkin and 1 comet in my 75 gal tank.

I have 2 new comets in quarantine in a 10 gal. They are all about 2" (+ tail).

They are all gorgeous and so cute and fun and  lovable  . I'm on vacation now and will post some pics next week. I should get an avatar too, when they're all together.

I'm not familiar with lighting, is this (the 6500k light) a fluorescent light?
Is fluorescent preferred to incandescent? Not sure what the proper lighting is for goldies and looking to purchase a tank + all the goodies

Fluorescent lighting is preferred because it doesn't heat the water.