usually the more dilute you use the developer the warmer it tends to be.
( or at least that is my experience ) i have left it in a tray, and it gets dark in color,
but works well still. even dark as cocacola it will work. i sometimes save a bunch of the
black stuff for processing paper negatives, or i use it in tandem with a coffee based developer
alternating between the 2 baths, sometimes i cut fresh developer with
the dark-stuff to take "the edge" off. i have only used it once until it was completely exhausted and it took
a long time to get that to happen.
i just opened another gallon ( i buy and mix 7 gallons at once ) it was mixed about a year ago, and
the prints i just posted in the gallery today were processed in it ...