To add your own colors on Android, first you have to tap on the edit button (paintbrush). Then, you will be able to see the colors button.

If you click on it, you will be able to add a color as an HEX code format. ex: ##FF7F50.

You can also, change the color of your texts. For this, you have to insert a text to a template and click on it to change the color or add a hex code color.