Burnt Umber's are dense permanent oxide pigments that will not fade.
This color is very important because this is the hue that yellow, yellow-orange, orange, orange-red and red become at their darkest.
I have noticed not only does it have a high absorption rate of oil, it also attracts mold and cracks. I saw this happen enough times in my friend's unvarnished work. Never leave an oxide exposed to air unvarnished.
A suitable replacement brown hue can be made with Burnt Sienna (which has a high silica count) plus Ultramarine Blue or Cobalt Blue mixed together.
Brown umber comes in many different colors. Different brands call the different colors different names. Raw umber is where this all begins.