Mockups can seem like an iceberg. There's so much beneath the surface in terms of advanced features. The features that seem to be hidden are learnable, but we don't surface them until you are ready to use them.
The app is designed this way on purpose to make only the properties available that are necessary for quick ideation. This tool is made for low-fidelity, and we're trying to protect designers, ourselves included, from getting precious. We believe that giving you fewer choices when you're ideating lets you focus on the ideas rather than the presentation, so the necessary attributes are properties, and sometimes the optional ones are available if you know how to use them.
One typical component that we hide text color properties on is the Arrow / Line component. Labeling is an option and most likely rarely used by the majority of our users. But if you wanted to color the text, all you would need to do is add the color macro to the input. So for red, use the hexadecimal color value #f0000 like so:
Let's look at that a little more closely:
There are other text formatting rules you can learn by checking out the Basic Text Formatting section of our documentation.