Add WHITE redaction colour

[xonoma]

Redactions are generally black in colour. But I propose adding white, as digital documents are often exported as PDFs rather than just scanned. For those, white is a sometimes more preferable colour for redactions.

[codecov[bot]]

Codecov Report

Merging #3 into master will increase coverage by <.01%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master       #3      +/-   ##
==========================================
+ Coverage   98.52%   98.53%   +<.01%     
==========================================
  Files           2        2              
  Lines         204      205       +1     
==========================================
+ Hits          201      202       +1     
  Misses          3        3

Impacted Files	Coverage Δ
marisol/marisol.py	98.5% <100%> (ø)	:arrow_up:

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