Q: I painted a flat sky using cobalt blue mixed with titanium
white. In daytime or combination light the sky still looks blue, but at
night with only artificial light the sky seems almost black. What’s
happening?
A: Both tungsten and artificial light project yellow, red,
and green, but very little blue. Natural light contains blue light. The
difference is enough to cause the appearance of near black under
incandescent light, even when cobalt blue is mixed with titanium white.
In addition, colors at that end of the spectrum are darker by nature.
Most gallery and museum lighting incorporates natural lighting or
full-spectrum bulbs to compensate for this fact. Beyond that, artists
need to either keep in mind the correct color impression and make the
necessary adjustments or accept it.