Why are the lines on my printout gray or very thin?

Gray lines

When Windows prints colored lines to a black and white printer, it attempts to represent the colors with shades of gray.  A colored line printed from VCADD will appear as gray line.  VCADD has an option on the Print dialog called All Colors to Black. When that option is enabled (its checkbox is ticked) all colors printed by VCADD will be black.

Thin lines

Thin lines are normally a result of of 0 (zero) width lines in VCADD.  For both the display and printing, a line width of 0 is interpreted as the "thinnest line that can be drawn".  On the display, that is one pixel, equivalent to a line width of 1. For printing it is determined by the printer and is often a single dot width.  It is not unusual for that to be 1/1200 inch or smaller.

The line widths which VCADD sends to the printer are determined by multiplying the line width number by the BaseLine Width set on the Print dialog.  Normally, that means that a line width of 0 will be printed with zero width.  The Lineweight 0 Has Width print option can be used to print width 0 lines as though they were width 1 lines.