The lower 3 bytes of this 32 bit field are used to specify a custom foreground text color as a set of RGB values. The low byte is the R (red) value, the second lowest byte is the G (green) value and the third lowest byte is the B(blue) value. The maximum for each field is 255. When all three are set to 255 (e.g. &h00FFFFFF) you get white; when all are set to 0 (e.g. &h00000000) you get black. However, to distinguish the latter case from the default (which is also &h00000000) you must set one of the bits in the upper byte to a non-zero value. For example, to set the text color to black, you might set TXC.FCOLOR to &h10000000. Since the default text color is black, this is not much of an issue, but the concept applies to all of the RGB-style color fields.
History
2021 March, A-Shell 6.5.1701: The automatic use of the Active Background Color (introduced in 6.5.1698.0) can now be overridden by setting one or more bits in the high byte of the TXC.bcolor field. Note that even though XTEXT treats a TXC.bcolor value of 0 as meaning "default" (i.e. white), 0 is technically the RGB value for black. So if you want to override the Active Background Color feature, so that the background remains white even when actively editing, then you should set TXC.bcolor explicitly to white (i.e. -1 or &hFFFFFFFF).
