1.30.4 Get methods

colour <-red: -> 0..255

colour <-green: -> 0..255

colour <-blue: -> 0..255

colour <-alpha: -> 0..255

The four 8-bit components of the colour's RGBA value. Triggers lazy resolution of a colour<-kind colour against the colour database on first access.

colour <-hue: -> 0..360

colour <-saturnation: -> 0..100

colour <-value: -> 0..100

Query the colour in the HSV (Hue/Saturation/Value) model:

• colour<-hue selects the basic colour (think of it as a position on the rainbow);
• colour<-saturnation is how intense the colour is — 0 is grey, 100 is fully saturated;
• colour<-value is brightness — 0 is black, 100 is white. HSV is more convenient than RGB for shading and palette arithmetic. Colours may be created in this space via colour->initialise with model=hsv. Reasoning in colour spaces is beyond the scope of this manual.

colour <-intensity: -> 0..255

Grey value of the colour, computed as the weighted average

(20*R + 32*G + 18*B) / 70

which closely matches ITU‑R BT.601 luma. Useful for converting colour to a monochrome substitute.

colour <-distance: colour|int -> int

Perceptual distance to the argument colour (or the encoded RGB integer), computed as CIEDE2000 ΔE₀₀ in CIE Lab space. Smaller is closer; values up to about 2 are considered visually indistinguishable.

colour <-hilite: factor=[ ->

0.0..1.0] -> colour

colour <-reduce: factor=[ ->

0.0..1.0] -> colour Return a lighter (colour<-hilite) or darker (colour<-reduce) variant. Used by class elevation to derive the lit and shadow sides of a 3-D box. 0.0 returns the colour unchanged; 1.0 returns white (colour<-hilite) or black (colour<-reduce). Defaults come from the hilite_factor / reduce_factor class variables.

The derived colour is associated with the original; asking for the same modification again returns the cached object, and destroying the original lets the derivative go.

colour <-convert: name -> colour

Type-checker hook. First looks the name up in @colours (already-constructed colours). Otherwise:

• If the name starts with # and has 3, 4, 6 or 8 hex digits after it, interpret it as a CSS hex literal:

  #c0453f -> R=192, G=69, B=63, A=255

  With three or four hex digits, each digit is doubled (#abc ≡ #aabbcc). With four or eight digits the trailing byte is the alpha channel.

• Otherwise the name is passed to the OS colour database for resolution.

colour <-lookup: [name|int], red=[0..360], green=[0..255], blue=[0..255], alpha=[0..255], model=[{rgb,hsv}] -> colour

Return an existing colour from @colours matching the arguments, or fail. Used internally to deduplicate equivalent colours; mirrors the signature of colour->initialise.

colour <-storage_reference: -> name

If the colour is colour<-kind, return its colour<-name. Otherwise return #RRGGBB (or #RRGGBBAA when alpha is not 255). The result is suitable as input to colour<-convert.

See also object<-storage_reference, object->save_in_file and source_sink<-object.