Differentiate between 4 categories (color problem)

I am wondering if there is someone who can help me to improve my application's user experience. I am developing a mobile e-learning platform which has 4 sections. I was asked to differentiate each section to be simple to memorise and be clearly visible. So I used different colors for each section as in the image below :

The problem here is that there is too much color which makes it difficult for the user to memorise sections and be comfortable with the application colors.

These are the product's pages.

As you can see there are a lot of colors which create vision problems; not only did I use 4 colors but also the primary color of the app (bleu) on every screen.

I am open to all suggestions in resolving this problem and make the design more professional.

Thank you for your help.