I've tried to make those kind of texts visible, by getting the notifications background a little darker, but it loses the nice look I wanted to get. So my only solution, for now, is to try getting the notifications background even darker, but I don't really want to do it.
If you could share some info with me, about how to change the text color, I will be really gratefull. As you could see, I'm just a Junior Dev, and this is my first Android Project, and I have a lot to learn. I will continue learning and trying to make this theme even better, but please, excuse me about that.
However, if you take a pair of seconds giving your phone a more detailed view, you will see the text in notifications, at least for now.
Thanks for using my theme. I'm glad about it, beacuse as I've said, it's my first project and many people are using it, it's a really big achievement for me. Thanks for undestanding.