Adding a banner image brings unwanted change in a section

Hi,

I have an issue which I am sure is very easy to fix, however I could not find any info on the forum so far and after trying some code injection did not get any result either.

Here is my problem:adding a banner image to a section is automatically changing the colour and style of my text and newsletter blocks within this section: I don't want that. How can I prevent this from happening or at least correct it.

Please find some screenshots below:

On the one hand, you can see on the upper screenshot that:
- [markdown] is blue
- [newsletter] title is black
- [newsletter] button is blue

On the other hand, on the below screenshot you can see that:
- [markdown] is blue (but only because I modified the code inside the [markdown], otherwise it would become white)
- [newsletter] title becomes white
- [newsletter] button becomes white

So far I did not succeed fixing that problem. Any help would be much appreciated please :)

Thanks in advance,

Thibaud