An RGB Device specification is identified by the prefix "rgb:" and has the following syntax:

rgb:red/green/blue

where red, green, and blue are encoded as h, hh, hhh, or hhhh, and h represents a single hexadecimal digit.

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Note: “h” indicates the value scaled in 4 bits; hh, the value scaled in 8 bits; hhh, the value scaled in 12 bits; and hhhh the value scaled in 16 bits, respectively. These values are passed directly to the X server, and are assumed to be gamma corrected.

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The eight primary colors can be represented as:

•Black: rgb:0/0/0

•Red: rgb:ffff/0/0

•Green: rgb:0/ffff/0

•Blue: rgb:0/0/ffff

•Yellow: rgb:ffff/ffff/0

•Magenta: rgb:ffff/0/ffff

•Cyan: rgb:0/ffff/ffff

•White: rgb:ffff/ffff/ffff

For backward compatibility, an older syntax for RGB device is supported, but its continued use is not encouraged. The syntax is an initial "pound-sign" character, followed by a numeric specification, in one of the following formats:

#rgb (4 bits each) #rrggbb (8 bits each) #rrrgggbbb (12 bits each) #rrrrggggbbbb (16 bits each)

The r, g, and b represent single hexadecimal digits. When fewer than 16 bits each are specified, they represent the most-significant bits of the value (unlike the "rgb:" syntax, in which values are scaled). For example, #3a7 is the same as #3000a0007000.

An RGB intensity specification is identified by the prefix "rgbi:" and has the following syntax:

rgbi:red/green/blue

The red, green, and blue are floating-point values between 0.0 and 1.0, inclusive. They represent linear intensity values, with 1.0 indicating full intensity, 0.5 indicating half intensity, and so on. These values will be gamma-corrected by Xlib before being sent to the X server. The input format for these values is an optional sign, a string of numbers possibly containing a decimal point, and an optional exponent field containing an "E" or "e" followed by a possibly signed integer string.

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Graphics Administration Guide for HP-UX 10.20