Which standard is recognized as the original scientific standard of color?

The correct choice is the spectrum because it serves as the foundational basis for the understanding of color in scientific terms. The spectrum refers to the visible light spectrum, which encompasses all the colors visible to the human eye, arranged in a specific order from red to violet. This natural phenomenon is a result of how light is refracted and absorbed by various materials, leading to the display of different wavelengths that correspond to different colors.

The other options, while relevant to color representation, are derived from the principles established by the spectrum. The RGB Color Model and the CMYK Color Model are both color systems used primarily in digital and print applications, respectively. The CIE Color Space, developed by the International Commission on Illumination, provides a standardized system for understanding color perception but is based on the earlier principles of the visible spectrum. Therefore, while these models and systems are important in their contexts, they all fundamentally rely on the original scientific standard of color represented by the visible light spectrum.