There is no color in Markdown itself. Where inline HTML styles survive, a span with a color works; GitHub strips styles, so the usual workaround there is LaTeX's \color inside math.
All ways to write it
Inline style. Stripped by GitHub and many hosted renderers.Needs HTML<span style="color:#c9372c">red text</span>
LaTeX color, in tools that render math (GitHub, Jupyter, KaTeX-based editors).Some tools only$\color{red}{\text{red text}}$
Example
You type
$\color{green}{\text{Passing}}$ and $\color{red}{\text{Failing}}$In a tool that renders math, this shows the two words in green and red. In one that doesn't, you see the raw LaTeX.
Questions
How do I color text in a GitHub README?
Inline styles are removed on GitHub. Use math: $\color{red}{\text{your text}}$. GitHub renders math with MathJax, which supports \color.
Can I highlight text in Markdown?
Some editors, including Obsidian, treat ==text== as a highlight. It is not part of CommonMark or GitHub Flavored Markdown; <mark>text</mark> is the HTML fallback.
Text color in Confluence
Confluence's editor has a text color menu, which is the simplest route on a page. Markdown Macro+ renders math with KaTeX, and KaTeX supports \color; check the result in the live preview before you save.