Anatomically-correct Kim Quy (Golden Turtle)

Question

The legend

The Kim Quy is a Vietnamese giant turtle god, whose specific trait is -you guessed it from the title- golden, supposedly living in and around waters, like the Hoàn Kiếm Lake where part of its myth takes place.

^{Depiction of Kim Quy and the Heaven's Will sword at the Hoàn Kiếm temple. From Wikimedia commons.}

It is known to appear in two of the Vietnamese legends. The first one is about an emperor receiving a mythical sword from Kim Quy, the second one another ruler who had troubles building his castle, whose Kim Quy also gave one of his claws to make a crossbow trigger. This crossbow was supposedly capable of firing many shots at a time and kill three hundreds soldiers with one press of the trigger.

I'd like to reproduce this turtle for my own world (without going into too much details, it would be an adventure guild's symbol with a quite similar legend). Now, since its golden appearance is perhaps the most difficult to reproduce biologically and its very identifying trait, this question will focuses on his unusual, golden appearance that I'd like to explain.

Therefore, how can a giant turtle appear golden?

The goal is very simple : Make a very big river turtle look as golden as possible so that its title "Golden Turtle" is well-deserved. The more you can make it look golden, the better. If you can make it of actual gold, I guess it's even better!

I do picture it is next-to-impossible to make a living being out of pure gold, so focus on what can be seen, then the insides after if you can. In the end, nobody in the legends would have dared to dissect the turtle, so who knows what its organs look like 🦋...

To further help, here's what I know about this turtle (and the minimal constraints you should follow) :

• Its exact size is not really told, but it is more often than not considered as being bigger than its normal counterparts like the "Hoan Kiem" turtle.
  • From my sources, it can at the very least carry a sword on its back, but in the tale I heard they went as far as telling it was the size of a small boat¹. If you can make it closer to the latter, it's nice as it would look more godly and mythical, but it's only a secondary, bonus objective. Focus on gold first.
• It has claws big and hard enough to make a functional crossbow trigger.
• It is able of swimming and diving underwater, so it shouldn't sink to the bottom :). The amount of time it can hold breath is unknown, but consider it should be long enough for a Kim Quy to approach and surface near an unaware Emperor on the shoreline. In order to give or reclaim a sword, for instance 🐢.
• Its diet is not really known. We just know it has become deep friend with a human, so it mustn't be too aggressive towards them.
• And of course, it's golden, especially the claws which is a key element of one of the legend. Answers which doesn't make the claw look golden won't fit the bill.

So how can we explain this turtle looks so much like gold?

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^{1 : Source (in French)}

Answer 1

Borrow from the jewel beetle.

To make it appear golden, I would take jewel beetles as example. Their coloration depends on structural coloration. Some look more metallic then others, some of them are yellow/golden.

So If a turtle has shell/claws outer layer composed of the same/similar structures as jewel beetles it could give the appearance of being metallic gold. However wouldn't affect the bulk properties of the shell, claw.

There is issue that it could be removed/damaged with physical wear/damage. But it is an example of giving the appearance of being metallic gold.