Fix for dimmed text on light color themes
The current implementation for DIM unconditionally makes the color darker. On light color themes the color is already black or near black and that produces a result which is not distinguishable from non-dimmed text. I believe that the original xterm implementation predates the usage of light color themes and that is the only reason not to address this.
This patch blends towards the background color and will produce a visually distinguishable result on all color themes. It will not work in case the color was already close to the background color but that does not matter in practice anyways.
This change was inspired by https://github.com/Tomas-M/iotop/issues/33
Patch: bbonev/vte@a7b70b2c