Science question about copper sulphate

Why do we see the solution of copper sulphate ⇦ on eBay or Amazon [affil link] blue? Is it because of reflection or transmission?

I recall seeing in a museum once a feather from a blue bird mounted on the wall of a display case with a light mounted behind the case and a small hole cut in the case behind the feather. When the feather was viewed in this transmitted light it was white, proving that there was no blue dye in the feather; rather, the blue color was a matter of refraction.

I suggest you position a strong light behind a beaker [beakers on eBay or Amazon [affil link] of copper sulphate in a darkened room, look through the beaker toward the light, and report what you find. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

SOLUTIONS ABSORB LIGHT FROM SUNLIGHT (ALL COLORS) AND THE COLOR YOU SEE IS THE LIGHT NOT ABSORBED BY YOUR SOLUTION. SO copper sulphate ABSORBS ALL COLORS (WAVELENGTH) OF SUNLIGHT EXCEPT BLUE. BLUE COLOR INCLUDE WAVELENGTH FROM ABOUT 450 TO 500 nm.

If you look your solution using red light you will see a black solution because all that light was absorbed.