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Red

Status: Experimental

present and registered, but lightly documented and not yet covered by dedicated tests.

Description

Red

The named colour RGBColor[1, 0, 0].

Examples (4)

Every input below was run against the current Mathilda build and its output recorded.

Applications (4)

The named primary evaluates straight to its RGBColor literal

In[1]:= Red
Out[1]= RGBColor[1, 0, 0]

An OwnValue, not an inert head -- it has already resolved

In[2]:= FullForm[Red]
Out[2]= RGBColor[1, 0, 0]

Usable wherever a colour directive is expected

In[3]:= Head[Graphics[{Red, Disk[]}]]
Out[3]= Graphics

An option value is a resolved colour too

In[4]:= FullForm[FrameStyle -> Red]
Out[4]= Rule[FrameStyle, RGBColor[1, 0, 0]]

Implementation notes

Definition. Red is one of Mathilda's named colour constants. It is not an inert head but an OwnValue: register_color("Red", rgb_color(1, 0, 0)) in graphics_init (src/graphics/graphics_init.c) binds the bare symbol Red to the literal RGBColor[1, 0, 0] and stamps it Protected. The docstring is kept centrally in src/info.c, beside CMYKColor, because info_init runs before graphics_init.

Representation. Evaluating Red yields RGBColor[1, 0, 0], so FullForm[Red] is RGBColor[1, 0, 0] and Head[Red] is RGBColor — the OwnValue has already fired by the time anything inspects the result. The helper color_component prints an exact 0 or 1 as a plain integer (matching Mathematica's own InputForm[Red]) and any other value as a real. The saturated primaries use RGBColor; the greyscale names (Black, White, Gray, LightGray) use GrayLevel.

Usage & limits. Because it resolves to a genuine colour literal wherever a bare argument is evaluated, Red works anywhere a style directive is expected — Graphics[{Red, Disk[]}], PlotStyle -> Red, an ArrayPlot cell, Directive[Red, Thick] — exactly as the long RGBColor[...] form would. Plot evaluates each option value once before storing it (split_options in plot.c), so Epilog -> {Red, ...} also sees the resolved literal. Red carries no opacity; use Opacity[a] or RGBColor[r, g, b, a] for a translucent colour.

Attributes: Protected.

References

Notes & additional examples

Notes

Red is the named colour RGBColor[1, 0, 0]. It is bound as a Protected OwnValue, not as an inert head, so it resolves to a real colour literal wherever a bare argument is evaluated: FullForm[Red] is RGBColor[1, 0, 0] and Head[Red] is RGBColor.

That is what lets it be dropped anywhere a style directive is accepted — inside Graphics, as a PlotStyle/Epilog/FrameStyle value, or in a Directive. The three exact-0/1 components print as integers, matching Mathematica's InputForm. Red carries no opacity; use Opacity[a] or the four-argument RGBColor[r, g, b, a] for a translucent colour.