Colour can be an aesthetic factor or it can have practical uses, such as signalling danger. It can also be used as a detection mechanism, such as the use of litmus paper to determine acidity levels.
A. Change the color of an object or its external environment.
- Use safe lights in a photographic darkroom.
B. Change the transparency of an object or its external environment.
- Use photolithography to change transparent material to a solid mask for semiconductor processing. Similarly, change mask material from transparent to opaque for silk screen processing.