I have not had a problem with black helmets being hotter, ventilation is way more important there.
The only thing I worry about is visibility, which has been mentioned above.
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1964 JRJ (Bob Jackson), 1973 Wes Mason, 1974 Raleigh Gran Sport, 1986 Schwinn High Sierra, 2000ish Colian (Colin Laing), 2011 Dick Chafe, 2013 Velo Orange Pass Hunter