RMarkdown: How to change the font color?

In RMarkdown is there a way to specify the font color?

There doesn't seem to be an option while browsing through the chunk options

The answer given at the link provided by @Ben Bolker:

Roses are <span style="color:red">red</span>, 
violets are <span style="color:blue">blue</span>.

does work if you select HTML (ioslides) as the output format.

However, it does not work if you select pdf (beamer) as output format. If you want to create a pdf, use LaTeX syntax:

    Roses are \textcolor{red}{red}, violets are \textcolor{blue}{blue}.

I create a function like this:

## Color Format
colFmt <- function(x,color) {
  
  outputFormat <- knitr::opts_knit$get("rmarkdown.pandoc.to")
  
  if(outputFormat == 'latex') {
    ret <- paste("\\textcolor{",color,"}{",x,"}",sep="")
  } else if(outputFormat == 'html') {
    ret <- paste("<font color='",color,"'>",x,"</font>",sep="")
  } else {
    ret <- x
  }

  return(ret)
}

Then you can use it inline like this:`r colFmt("MY RED TEXT",'red')`, and colored text will be rendered regardless of whether working on latex or HTML document.

This seems to work very well in both output formats, pdf and html:

Roses are $\color{red}{\text{beautiful red}}$, 
violets are $\color{blue}{\text{lovely blue}}$.

Hope it helps.

An output-format agnostic solution would be to use the dedicated text_spec() function in the kableExtra package:

Roses are `r kableExtra::text_spec("red", color = "red")`,

violets are `r kableExtra::text_spec("blue", color = "blue")`

Others have provided answers for output other than Word. For Word, you can use the Pandoc custom-style syntax to accomplish this with the aid of a reference word document. First, inside your reference.docx template, create a new Word style with a short, distinct name. If you want your font color to apply to a full paragraph, you can use the default, “Linked Paragraph and Character” style type. If you only want to emphasize some words in a paragraph with color, you need to select the “Character” style type. Change the font color (and any other styling you need) and save the reference.docx file.

Then, inside your .Rmd file, you can use the tag as follows:

<div custom-style=“DivCol”>Whole paragraph of colored text</div>

Just a <span custom-style=“SpanCol”>few words</span> of colored text

A word regarding style names - for reasons I don’t understand, this process did not work with the style name “Span_Add” but “SpanAdd” was fine.

I basically used Nicholas Hamilton's answer but because I used xtable and print, I had some problems with certain latex sequences being escaped. Namely, \\textcolor being transformed to $\backslash$textcolor. I was able to get it right by avoiding sanitizing in the following way:

```{r results='asis'}
tbl = data.frame(a = letters[1:10], b = 1:10 / 10)
tbl$b = ifelse(tbl$b < 0.5, colFmt(tbl$b, "red"), colFmt(tbl$b, "green"))
print(xtable(tbl), sanitize.text.function = identity)
```

I then had to go and manually sanitize a few characters like % but at least \textcolor was correctly applied. Of course, this could be avoided by expanding your own sanitize function.

For PDF and HTML, to get colored text which you can modify with markdown highlighting : see the rmarkdown book. Pandoc filter is the best choice.

For Microsoft word, you have to create first a Template_MS.docx with custom styles. Warning: create different styles for coloring paragraphs (paragraph style) and for colorings few words (character style). It is an option when you made a new style.

Add in th YAML:

---      
output:   
 word_document:   
    reference_docx: Template_MS.docx   
---   

And next:

For <span custom-style="Character1">few words</span> of colored text.

For paragraph.

<div custom-style="Paragraph1">Paragraph of colored text. Blabla. Blabla.</div>   

Nota Bene:

• Do not use the same style for Paragraph and a few words, it is bugging.

• If it is not working, check that your style is for paragraph ou character in MS.

• If it is not working, install an updated version of pandoc.

Easily change the font color with sass

There's a new and better way of specifying colors or fonts in R Markdown:

• Download the package sass
• Create a chunk in your RMarkdown document with the following options {sass, echo = FALSE}
• include the following SASS code in that chunk:

// This chunk contains SASS-code to specify font color

h1, h2, h3, h4, h5
  color: blue // Color for the headers

body
  color: red // Color for the text in the main part of your document

// The colors are only examples. You can change them to anything. You could also use hex codes.

You can also change much more than just the font color

Typically, I include something like this in my documents, to also change the font type, the sizes, the link colors etc.:

// These are variables, and are easy to change
$color: blue
$color2: red
$font: "Arial"
$font-size: 16px

h1, h2, h3, h4, h5
  color: $color
  font-family: $font
  font-weight: bold

body
  background-color: white
  color: black
  font-family: $font
  font-size: $font-size

a
  color: $color

a:link
  color: $color

a:hover
  background-color: $color2

You can change any HTML tag you can think of this way.

Read more about SASS here.