d.grid overlays a grid on the display monitor. You can specify grid size (in map units), color and origin.
d.scale displays a scale bar with north arrow on the display monitor. You can specify background and bar/text color, specify a map location or use the mouse to locate the scale bar on the monitor. Kind of klunky.
d.label creates and places single-line text labels on the display monitor. You can choose background and text colors, font and text height (specified as percent of monitor height).
d.text displays text in the display monitor. You usually create a text file with format codes first, and then redirect it to d.text. A text file example:
.C red # text color red
.S 10 # text height 10 % of monitor height
.F romanc # font
.B 1 # bold on
# (skips top line)
GRASS Demo # space-indented text for second line
.S 6 # smaller text
.C blue # text color blue
.B 0 # bold off
Spatial Analysis Lab # space-indented text for third line
....
Save this as textfile, then run d.text < textfile
Getting centered text takes some trial and error, and requires a consistent display monitor aspect ratio (height/width). If you re-dimension your monitor, you will have to re-center your text.
You can check out GRASS's font options with d.font.
d.colormode determines whether maps are displayed with their own color tables or the fixed color table of the graphics monitor. The default colormode is "fixed," but some modules such as i.vpoints will change the colormode to "float." Many X-terminals will have unstable colors under a float colormode. When changing color tables with the interactive d.colors module, you should change the colormode to float and d.erase the monitor first.
Color tables for your own raster maps are located in the colr directory under your mapset. If you alter the color table of some other user's raster map, this will be stored under the colr2 directory in that user's mapset.
The default color table for a GRASS raster map is the standard digital elevation model scheme. To edit raster map color tables--
r.colors provides a menu of color schemes, including greyscale, histogram-equalized greyscale, rainbow and random. You can define your own color rules, specifying colors by name or RGB triple for specific cell values, or ramp colors over ranges of cell values.
d.colors supports interative manipulation of colors for individual cell values, displaying the colors as they are altered. Change your monitor's colormode to float and erase it before running d.colors. Use the u and d keys to cycle through the range of category values. The r/R g/G and b/B keys decrease/increase red, green and blue intensity for the color of the current category. The h key highlights cells in the current category. The c key saves the revised color table; the Q key quits the module.
d.measure measures distances in map units between mouse clicks on the monitor display.
d.geodesic displays great-circle paths and measures great-circle distances between two mouse clicks on the monitor display. (Only works with lat-long locations).