RStudio themes when using Markdown

[leok31]

I know that the latest RStudio allows you to import custom themes from sites like tmtheme-editor.herokuapp.com.
But so far I have not been able to make those themes work for when I'm using Notebook mode. The theme editor does not recognise text that is inside ```{r} chunk.
Is there a way to get a theme that would change how the code looks like inside the chunks while I'm writing the code, not when it is converted to HTML.
For example, if I have some code like this:

```{r}
plot(cars)

Is there a way to have the plot() function be red for example?

[kevinushey]

Within:

Tools -> Global Options... -> Code -> Display

There is a setting:

Highlight R function calls

If you check that, a highlight rule for function calls will be turned on. Such tokens will have a class of the form identifier.support.function. Custom themes can provide styles for that particular set of classes as appropriate.