# [R] col2rgb() function

David Stevens d@v|d@@teven@ @end|ng |rom u@u@edu
Sun Jul 23 23:35:52 CEST 2023

```Nick,

I've also made colors transparent by pasting the hex equivalent of, say,
0.3*256 = 76.9 to the hex color code. e.q. for black it might be
"#0000004d" and the 4d is 77 in hex. That way you don't need to convert
back and forth so much. If col is "#000000" the transparent version is

tcol <- paste0(col,"4d")

This would work in one step on a whole palette.

David

David K Stevens, PhD, PE, Professor
Civil and Environmental Engineering
Utah Water Research Laboratory
Utah State University
8200 Old Main Hill
Logan, UT 84322-8200
david.stevens using usu.edu
(435) 797-3229 (office)

On 7/23/2023 1:00 PM, Nick Wray wrote:
> Thanks That works nicely  Nick
>
> On Sun, 23 Jul 2023 at 19:26, Ben Bolker <bbolker using gmail.com> wrote:
>
>>
>> cb8<- c("#000000", "#E69F00", "#56B4E9", "#009E73","#F0E442", "#0072B2",
>>      "#D55E00", "#CC79A7")
>> plot(0,0,xlim=c(1,8),ylim=c(0,1))
>> points(1:8,rep(0.5,8),col=cb8,pch=19,cex=2)
>> points(1:8,rep(0.75,8),col=adjustcolor(cb8, alpha.f = 0.3), pch=19,cex=2)
>>
>> On 2023-07-23 2:15 p.m., Nick Wray wrote:
>>> Hello  I have a palette vector of colour blind colours (in hexadecimal)
>>> which I’m using for plots, but they are not see-through, and as I wanted
>> to
>>> overlay some histograms I wanted to convert these colours to rgb, when
>> you
>>> can set the opacity.
>>>
>>> I have found the function col2rgb(), which works in the sense that it
>> gives
>>> a vector of numbers but these don’t work directly in rgb because they are
>>> too big.  If I divide through to make them all less than 1 I don’t get
>> the
>>> corresponding colour-blind hue, but something somewhat off.
>>>
>>> Here is the colour-blind palette in a plot:
>>>
>>>
>>> *cb8<- c("#000000", "#E69F00", "#56B4E9", "#009E73","#F0E442", "#0072B2",
>>> "#D55E00", "#CC79A7")*
>>>
>>> *plot(0,0,xlim=c(1,8),ylim=c(0,1))*
>>>
>>> *points(1:8,rep(0.5,8),col=cb8,pch=19,cex=2)*
>>>
>>>
>>>
>>> so if I try to convert the red dot ("#D55E00") (number 7) I get
>>>
>>> *col2rgb("#D55E00"*
>>>
>>>     [,1]
>>>
>>> red    213
>>>
>>> green   94
>>>
>>> blue     0
>>>
>>> *points(7,0.25,col=rgb(rgb(213,94,0)),pch=19,cex=2)*
>>>
>>> gives me an error message and although if  I divide through
>>>
>>> *points(7,0.25,col=rgb(213/307,94/307,0),pch=19,cex=2)*
>>>
>>> gives me a reddish dot, but not the same as in the colour-blind palette
>>>
>>>
>>>
>>> Somewhat mystified.  Can anyone help?? Thanks Nick Wray
>>>
>>>        [[alternative HTML version deleted]]
>>>
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>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>> and provide commented, minimal, self-contained, reproducible code.
>>
> 	[[alternative HTML version deleted]]
>
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