注：定义符合ISO/CD 10303-46:1992
颜色rgb作为颜色规格的一个子类型，由rgb颜色模型中红色、绿色和蓝色的三个颜色分量值定义。
注：与通常颜色分量的值范围为0…255之间的整数相反，ISO10303-46中的定义将颜色分量定义为0.0…255之间的实数。。。1.0. 应用程序需要在填充颜色RGB值之前执行此转换。
注意对应的步骤名称：colour\u rgb。name属性已被省略，reg、green和blue部分的数据类型为IfcNormalizedRatioMeasure，它已经包括值的范围限制。正式标准的最终定义请参考ISO/IS 10303-46:1994，第138页。
IFC2x2中增加的新实体。
Attribute inheritance
| # | Attribute | Type | Cardinality | Description | C |
|---|---|---|---|---|---|
| IfcPresentationItem | |||||
| IfcColourSpecification | |||||
| 1 | Name | IfcLabel | [0:1] | Optional name given to a particular colour specification in addition to the colour components (like the RGB values).
EXAMPLE Names of a industry colour classification, such as RAL. |
X |
| IfcColourRgb | |||||
| 2 | Red | IfcNormalisedRatioMeasure | [1:1] | The intensity of the red colour component.
NOTE The colour component value is given within the range of 0..1, and not within the range of 0..255 as otherwise usual. |
X |
| 3 | Green | IfcNormalisedRatioMeasure | [1:1] | The intensity of the green colour component.
NOTE The colour component value is given within the range of 0..1, and not within the range of 0..255 as otherwise usual. |
X |
| 4 | Blue | IfcNormalisedRatioMeasure | [1:1] | The intensity of the blue colour component.
NOTE The colour component value is given within the range of 0..1, and not within the range of 0..255 as otherwise usual. |
X |
EXPRESS Specification
ENTITY IfcColourRgb
SUBTYPE OF (IfcColourSpecification);
Red : IfcNormalisedRatioMeasure;
Green : IfcNormalisedRatioMeasure;
Blue : IfcNormalisedRatioMeasure;
END_ENTITY;
原文：https://www.cnblogs.com/herd/p/14214393.html