This is the guide that I use: https://www.markdownguide.org.
There is nothing out of the box to will enable you to colour text, and so yes, this will get you into the realm of custom CSS or mixed mode (incorporating HTML) which will break the beautiful simplicity of MD, and I’d expect that the different flavours of md will not all play nicely with the various md editors, DT included.
There are some great examples of using CSS to style md on this forum, especially the guides written by @chrillek : CSS for Markdown – the series.
My simple go-to solution that I actually use a lot to make text jump out is highlighting. The extended markdown syntax states that ‘some Markdown processors allow you to highlight text’. Here is what this will look like in DT:
