| 摘要 |
Systems and methods for providing a machine readable colored envelope and systems and methods for processing such envelopes are described. In certain examples, the machine readable colored envelopes are colored using a reversible negative photochromic colorant that bleaches when exposed to an activation energy such as ultraviolet radiation and returns to its original color after the activation energy is removed. In another example, the colorant has more than one stable color state.
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