Check if character string is a valid color representation

Question

Short question, if I have a string, how can I test if that string is a valid color representation in R?

Two things I tried, first uses the function co

Answer 1

Update, given the edit

?par gives a thorough description of the ways in which colours can be specified in R. Any solution to a valid colour must consider:

1. A named colour as listed in colors()
2. A hexademical representation, as a character, of the form "#RRGGBBAA specifying the red, green, blue and alpha channels. The Alpha channel is for transparency, which not all devices support and hence whilst it is valid to specify a colour in this way with 8 hex values it may not be valid on a specific device.
3. NA is a valid "colour". It means transparent, but as far as R is concerned it is a valid colour representation.
4. Likewise "transparent" is also valid, but not in colors(), so that needs to be handled as well

5. 1 is a valid colour representation as it is the index of a colour in a small palette of colours as returned by palette()

   > palette()
   [1] "black"   "red"     "green3"  "blue"    "cyan"    "magenta" "yellow" 
   [8] "gray"
   

   Hence you need to cope with 1:8. Why is this important, well ?par tells us that it is also valid to represent the index for these colours as a character hence you need to capture "1" as a valid colour representation. However (as noted by @hadley in the comments) this is just for the default palette. Another palette may be used by a user, in which case you will have to consider a character index to an element of a vector of the maximum allowed length for your version of R.

Once you've handled all those you should be good to go ;-)

To the best of my knowledge there isn't a user-visible function that does this. All of this in buried away inside the C code that does the plotting; very quickly you end up in .Internal(....) land and there be dragons!

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Original

[To be pedantic #000000 isn't a colour name in R.]

The only colour names R knows are those returned by colors(). Yes, #000000 is one of the colour representations that R understands but you specifically ask about a name and the definitive list or solution is x %in% colors() as you have in your second example.

This is about as stable as it gets. When you use a colour like col = "goldenrod", internally R matches this with a "proper" representation of the colour for whichever device you are plotting on. color() returns the list of colour names that R can do this looking up for. If it isn't in colors() then it isn't a colour name.