Inorganic Compounds and Color

The human eye perceives a mixture of all the colors, in the proportions present in sunlight, as white light.
Complementary colors, those located across from each other on a color wheel, are also used in color vision.
- The eye perceives a mixture of two complementary colors, in the proper proportions, as white light.
Likewise, when a color is missing from white light, the eye sees its complement.
- For example, when red photons are absorbed from white light, the eyes see the color green.
- When violet photons are removed from white light, the eyes see lemon yellow
An object is black if it absorbs all colors of light.
An object is white if it reflects all colors of light
An object has a color if it absorbs all colors except one

The blue color of the [Cu(NH3)4]2+ ion results because this ion absorbs orange and red light, leaving the complementary colors of blue and green.
If white light (ordinary sunlight, for example) passes through [Cu(NH3)4]SO4 solution, some wavelengths in the light are absorbed by the solution.
The [Cu(NH3)4]2+ ions in solution absorb light in the red region of the spectrum.
The light which passes through the solution and out the other side will have all the colors in it except for the red.
We see this mixture of wavelengths as pale blue (cyan).
The partially filled d orbitals of the stable ions Cr3+(aq), Fe3+(aq), and Co2+(aq) give rise to various colors.
Non-transition metal ions in water: appear clear/transparent
Transition metal ions in water: produces various colors