Antique cameo were made from various materials. Conch shell cameo, were mainly carved in Italy, and are an orange/ brown color with the foreground color of the subject predominately white. How a cameo carver "plays" with the colors of the material in carving and breathing life into the subject is often a secondary consideration. I feel this aspect of a cameo beauty, is the most important.
Composite cameos were produced in large numbers, so it is important to determine if the a cameo is real shell or made from composite material. You will notice there is no "play-of-color" in the cameo below. The color is uniform. This image of a composite cameo, is an example of a faux cameo.
I'm leaning towards conch shell, for your cameo lovely. Do you know what metal the surround is made from? Are there any markings on the mount? Concerning the value of your cameo, you would need to get an expert appraisal carried out which is possible through Antique Jewelry Investor.
