* Add colors utilities
Local function get_base_color(), conversions hex <=> rgb, rgb color mixer, and global function get_color()
* Round numbers to avoid eventual float in string.format
* Simplify inbox/outbox mixing of color
Use a single if statement for each property and concatenate to displayed_color then execute mail.get_color(displayed_color) instead of making many combined if statements
* Convert 3-chars hex colors to 6-chars hex colors
Could break the code, the hex convert to rgb always run on 6-chars
* Rework color utility using tables
Instead of one-letter symbols, it now supports tables of identifiers or single strings
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