In the first line, change:
set( "sim/private/controls/light/random_percent=", 0.10)
to:
set( "sim/private/controls/light/random_percent", 0.10)
(get rid of that equal sign)
No worries, thanks for the reply. I've been using "Chilled Air" during the winter months here, so will start trying out other color schemes as Spring approaches.