I spilled bleach on my pants. The exposed area turned from grey to orange. Why orange of all colours?
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Light is made of different wavelengths that we detect as different colors. Going from long wavelength to short wavelength we have ROYGBIV (red orange yellow green blue indigo violet). Things that are colored absorb some wavelengths and reflect others. For example, an orange thing absorbs RYGBIV but reflects Orange. A green thing absorbs ROYBIV but reflects green. Black (and grey) things absorb all wavelengths of visible light; white things don’t absorb any of the wavelengths.
We use colored things that bind to fabrics as dyes. At the chemical level, the dyes that absorb long wavelengths have longer regions of what are called conjugated bonds. I’m not sure what an ELI5 synonym for ‘conjugated bonds’ is, but it doesn’t actually matter if you know what a conjugated bond is to understand this. Things that absorb shorter wavelengths have shorter lengths of these chemical bonds.
The bleach acts on some of the conjugated bonds, which are present in the longest stretches in red dyes, (long stretch = big target vs little target) thus red dyes are more likely be affected …..making the pants look orangey-brown. Some shorter stretches of the red dyes might remain and still absorb shorter wavelengths.
The same thing happens when dark-haired people bleach their hair – at first it turns orange.
Successive treatments with bleach will make it lighter and lighter.
A little off-topic, but people do what you have done intentionally (bc obv it looks cool) in a process called reverse tie dye. It is a lot like tie dye, but you fold/wrap/tie the fabric to limit the penetration of the bleach.
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