Why does Clemmys guttata have spots?

When I look for the Clemmys in the pond, I look for yellow spots.  When they swam under the ice, it was the spots that took my attention. The spots make finding the Clemmys easier. Yellow is the color that constrasts more on black, to the extent that other animals, such as wasps or fire salamanders,  use this combination as an aposematic coloration, a warning to potential predators.
Other turtles also have spotted carapaces, such as Emys orbicularis or Emydoidea blandingii. Are the spots  just a nature caprice or there is another reason for it?

When they are wet the colors are more stunning

Yellow spots help me to find them when they are inside the filamentous algae

Good camouflage, but do the spots help in it or just  do the opposite?

When they are dry the color is duller. Good comouflage on this substrate

The predominant color in Clemmys guttata is black, and it is probably related with thermoregulation. They use to live in cold places and it is one of the first turtles to emerge in spring. Then the black color is an advantage.

Regarding the yellow spots, in the book Turtles of the United States and Canada it says they could imitate duckweed  (Lemna sp) and other acquatic plants common in the wetlands that this species inhabits, making detection by predators more difficult. I found a paper on the subject

http://profile.usgs.gov/myscience/upload_folder/ci2012Nov2415261433446Duckweed%20and%20turtles.pdf

Looking for information about camouflage, it says that in very vegetated habitats, such as jungles or forests, the combination of filtered light with the ground, plants, stones, trunks...makes a spotted or stripped animal  less defined, its shape fades with the environment (young deer, felines...)

Is it possible then that the spots are useful for camouflage? In the pond where I have them they have the opposite effect, they make the turtle more visible. Do they make them more unnoticed in their natural habitat? I don't have the answer, but to assess camouflage you have to see the animal in the habitat. I saw it very clearly with   Testudo hermanni. This tortoise in a garden stands out, but in the habitat it is different

In the middle, it is difficult to see its shape

They are not always so well hidden, but they still ressemble the tones of the environment.

So, it would be interesting to see the Clemmys in their habitat, underwater and in land, to check if the spots help to make them unnoticed.

I have seen some pictures of the different type of wetlands in internet: vernal pools, marshes, swamps, bogs, fens... Some links with descriptions and pictures  of the different types.

http://www.personal.ceu.hu/students/03/nature_conservation/wwddetail/Types_classif.html

http://mnfi.anr.msu.edu/abstracts/ecology/vernal_pool.pdf

http://www.fcps.edu/islandcreekes/ecology/marsh.htm

http://education.nationalgeographic.com/education/encyclopedia/swamp/?ar_a=1

http://www.nhptv.org/natureworks/nwep7i.htm

It would also be interesting to see things from the perspective of their predators (racoons, skunks, otters...). We are a very visual species, we see in detail and many colors. Other species see differently. In a conference done  by the Societat Catalana d'Herpetologia (SCH), one talk was about sight in wall lizards. These lizards, like chelonians, see down to the UV spectrum. Females see tones in males that we don't perceive. The speaker talked about antropomorphism by omission: the one that takes place when by deffault we assume that the sensory abilities of the species that we study are similar to ours.
This is a link to the study, but I only found it written in Catalan.

http://roderic.uv.es/bitstream/handle/10550/23877/tesi_GuillemP%C3%A9rez_deLanuza.pdf?sequence=1

I remember a conversation with a  biologist that studies T. hermanni in the wild. Once they used trained dogs to count the number of tortoises in a territory.  He realized how differently do humans and dogs use vision. The dog was searching by scent and although it often passed near tortoises that the human eye catched easily,  the dog didn't see them. He found them by scent.

Something similar happens with cats.  Sometimes a cat sees a dog at some distance and stays completely quite, frozen. Very often the dog passes by without seing it. We, humans, use to see it.