How to Set Entity Colour

Quick answer: Colour determines how an entity displays on screen and how it prints. New entities take on the current colour, set by CECOLOR. You can choose from 255 index colours or define a true colour, and whether an index-coloured entity actually prints in that colour depends on the plot style table you’re using.

Index Colours

An 8-bit value allowing up to 256 possible colours, each with a unique number from 1 to 255. Seven have names too: red (1), yellow (2), green (3), cyan (4), blue (5), magenta (6), and white/black (7). Index colour 7 is special, it displays white on a black screen background and black on a white one, adapting automatically, but it always prints black regardless.

ByLayer and ByBlock as Colour Numbers

ByLayer and ByBlock are technically colour numbers themselves: ByLayer is 256, ByBlock is 0. Anywhere you’d specify a colour, you can use either name or its corresponding number interchangeably.

The Four Colour Options

• ByLayer: entities take on their layer’s colour, so changing the layer’s colour changes every entity using it at once.
• ByBlock: entities draw in index colour 7 (black or white, depending on the screen background) until they’re included in a block definition; once that block is inserted into a drawing, they adopt the block’s colour instead.
• Index Colour: any of the 255 numbered colours.
• True Colour: a specific RGB-defined colour.

Whether Index Colours Actually Print As Shown

This depends on the Colour Table (CTB) or Style Table (STB) used for printing. The printed colour only matches the entity’s actual colour if that CTB or STB’s Colour setting is set to Use Object Colour, otherwise the plot style table can override or remap it for printing.

True Colours

A 24-bit value, allowing up to 16,777,216 possible colours, defined using RGB (red, green, blue), each ranging from 0 to 255. Black is (0,0,0), white is (255,255,255). The number of bits defining a pixel’s colour shade is called its bit-depth; some newer display systems offer a 32-bit mode, where the extra byte (the alpha channel) handles control and special-effects information rather than adding more colours.

Setting the Current Entity Colour

1. Open the Color dialog: run COLOR, click the Select Color tool on the Settings toolbar, choose Color in the Properties panel and select Select Color from the dropdown, or double-click the Color field in the Status Bar.
2. On the Index Color tab, either click a coloured tile or type a colour number directly.
3. On the True Color tab, either click within the Color Selection panel or set the RGB values directly in the Color Parameter fields.
4. Click OK to confirm.

Frequently Asked Questions

Does index colour 7 always look the same? On screen, it adapts to your background, white on black, black on white, but it always prints black regardless of screen background.

Why doesn’t my entity print in the exact colour it displays as? Check the Colour Table (CTB) or Style Table (STB) being used to print. Unless its Colour setting is Use Object Colour, it can remap the printed colour away from the entity’s actual one.

What’s the numeric equivalent of ByLayer and ByBlock? ByLayer is colour number 256; ByBlock is colour number 0. Either the name or the number works anywhere a colour is specified.

How many colours does true colour actually support? Up to 16,777,216, using a 24-bit RGB value with each of red, green, and blue ranging from 0 to 255.