"Epigenetics is the study of heritable changes in gene expression that occur without altering the underlying DNA sequence. These changes, also known as epigenetic modifications, affect how genes are turned "on" or "off" and are influenced by factors like environment, lifestyle, and aging."
That's a separate effect, known as acromelanism, or "point coloration". It's the result of an enzyme which is inactivated by higher temperatures, not a genetic change - the extent of pointing can change over an animal's lifetime, and the specific pattern isn't inherited. (For instance, if you somehow convinced a cat with color pointing to wear a sweater, its fur would stay light under that sweater, but any offspring it had would not inherit that pattern.)
That isn't a genetic change either, though. Those species of turtle either lack the typical sex-determining chromosomes entirely, or have sex-determining chromosomes which can be inactivated during development. The genotype doesn't change as a result of what temperature the egg is incubated at; its expression does.
"Epigenetics is the study of heritable changes in gene expression that occur without altering the underlying DNA sequence. These changes, also known as epigenetic modifications, affect how genes are turned "on" or "off" and are influenced by factors like environment, lifestyle, and aging."