Color aesthetic mapping syntax

[Mattriks]

The current syntax that is allowed for color mapping includes:

• color=[colorant"red"] (works with some, but not all, Geoms)
• color=["group label"] see example here
• color="population" or color=:population # refers to a column in a DataFrame
• color=3 # refers to a column in a DataFrame
• color=Col.value() or color=Col.index() for wide-format data

So color="red" has multiple possible meanings.
Here and below are options for a new syntax.

Option 1)

• color=["red"] (also color=[1]) are always group labels, and color="red" is a color or dataframe column

[Mattriks]

Another example to keep in mind is linestyle=[:dash], which could be interpreted as a categorical or functional variable.

[Mattriks]

Option 2 (typed"string" only syntax)

• color=colorant"red" and linestyle=linestyle"dash".

[knuesel]

What about the following?

• color="red" and color=:red refer to DataFrame columns
• color=["red"] refers to a group label
• color=[:red] refers to a predefined color
• color=RGB(1,0,0) color=[RGB(1,0,0)] can be used to specify an arbitrary color

The first point seems important to me for consistency with other aesthetics and DataFrame indexing.

[knuesel]

I think my previous idea is too inconsistent with how aesthetic=[...] generally works (I didn't realize that color=["red"] works like a DataFrame column with automatic cycling).

Much better to keep the current behavior, where color=[...] treats [...] the same as if it was a DataFrame column (if I understand correctly).

I like option 2, maybe with a shorthand const var"@c_str" = var"@colorant_str" so we can write color=c"red".