There are two things that you can do to make sure that your choice of colour in your service communication (be it paper stuff or digital stuff) doesn’t make it all illegible:

The difference in brightness between the background colour that you use and the text that sits on that background has to be big enough so that people can differentiate both. There are free tools that tell you if your colour contrast is high enough

A good chunk of the population has some sort of colour blindness (about 8% of men and 0.5% of women). The tool Color Oracle lets you simulate how a person who is colour blind would see your design. The nice thing about that tool is that it simulates different types of colour blindness and gives you an estimate of the percentage of people affected by it.