Blue ink appears black on an orange sticky note due to the way the human eye perceives colors and the properties of the ink and paper involved.
When white light (which contains all colors of the visible spectrum) shines on an object, the object absorbs certain colors of light and reflects others. In the case of an orange sticky note, the paper absorbs most colors of light and reflects primarily orange light.
Blue ink, on the other hand, absorbs most colors of light except for blue, which it reflects. When blue ink is applied to an orange sticky note, the ink absorbs most of the orange light that the paper reflects, but reflects blue light, which our eyes perceive as black in this context.
Therefore, the blue ink on an orange sticky note appears black because it is absorbing most of the orange light that the paper reflects and is reflecting only the blue light that our eyes perceive as black in this context.
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