by Ralph Grabowski

All current CAD packages give you the freedom to use many colors in a drawing. Whereas CAD systems of yesteryear limited you to 255 or even just fifteen colors, today's CAD systems support the 16.7 million colors. That leaves new CAD users in a quandary: What color coding system? Why use colors at all?

Color was rarely used in manual drafting, so you may question the thought of using color in an electronic drawing. Feel free to do so. Since the output from a CAD system is, in most cases, a black-white plot, you may not want to use color.

The Case for Color

CAD programs use color for two purposes: (1) operator cues, and (2) controlling the plotter.

When a drawing contains colored elements, the colors provide cues to the operator, making him or her more efficient. It's easier to pick out a blue water pipe from a sea of red structural members than when pipes and steel beams are both drawn in black.

While a structural engineering firm may decide against a color display, they still need to use color in drawings — even if the colors are not displayed or plotted. That's because all CAD systems use color to control the plotter's pens.

When it comes time to plot the drawing, the CAD program asks you to map color numbers to the plotter's pen numbers. To help you decide how to use colors in a drawing, here are some ways you can map colors to pen numbers:

This article is excerpted from CAD Manager's Guidebook by Ralph Grabowski, with permission of the publisher, OnWord Press, an imprint of Thomson Learning.

Consumer-oriented CAD systems, such as FloorPlan 3D, preassign colors and textures to predrawn objects. Other CAD systems use color numbers to assign textures to surfaces. Image: Ralph Grabowski Assigning colors to layers via an AutoCAD dialog box. Image: Autodesk, Inc.   Click on thumbnail images to view full-size pictures.