choose two that are red and sweet

Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associated with objects or materials based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates.

Because perception of color stems from the varying spectral sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of color, however, do not fully explain the psychophysical perception of color appearance.

Color science includes the perception of color by the eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range (i.e. light).

Color of objects

The color of an object as perceived by an observer is not an intrinsic quality of that object, but depends on several factors:

the physics of the object (which wavelengths of light are selectively absorbed, reflected, transmitted, or emitted)
the color of the light shining on the object (color cast of the illuminant)
the angles between observer, object and illuminant (applicable to structural color)
the physics of light in its environment (how the atmosphere may affect the light through Rayleigh scattering or dispersion, for example)
relative velocity between object and observer (red shift; mostly applicable to astronomy)
the characteristics of the perceiving eye (the number and spectral sensitivity of cone classes and dimensionality of color vision)
higher order processes in the brain that affect the color, such as color constancy

Some generalizations of the physics can be drawn, neglecting perceptual effects for now:

Light arriving at an opaque surface is either reflected "specularly" (that is, in the manner of a mirror), scattered (that is, reflected with diffuse scattering), or absorbed—or some combination of these.
Opaque objects that do not reflect specularly (which tend to have rough surfaces) have their color determined by which wavelengths of light they scatter strongly (with the light that is not scattered being absorbed). If objects scatter all wavelengths with roughly equal strength, they appear white. If they absorb all wavelengths, they appear black.
Opaque objects that specularly reflect the light of different wavelengths with different efficiencies look like mirrors tinted with colors determined by those differences. An object that reflects some fraction of impinging light and absorbs the rest may look black but also be faintly reflective; examples are black objects coated with layers of enamel or lacquer.
Objects that transmit light are either translucent (scattering the transmitted light) or transparent (not scattering the transmitted light). If they also absorb (or reflect) light of various wavelengths differentially, they appear tinted with a color determined by the nature of that absorption (or that reflectance).
Objects may emit light that they generate from having excited electrons, rather than merely reflecting or transmitting light. The electrons may be excited due to elevated temperature (incandescence), as a result of chemical reactions (chemiluminescence), after absorbing light of other frequencies ("fluorescence" or "phosphorescence") or from electrical contacts as in light-emitting diodes, or other light sources.

To summarize, the color of an object is a complex result of its surface properties, its transmission properties, and its emission properties, all of which contribute to the mix of wavelengths in the light leaving the surface of the object. The perceived color is then further conditioned by the nature of the ambient illumination, and by the color properties of other objects nearby, and via other characteristics of the perceiving eye and brain.