Indesign highlighted text red/pink

All I do is pick another font, then repick the one you want.. and it works. 

This one got me pulling my hair and i can't afford to lose more time . I have to abandon the search for now.

In following screenshot:

• No paragraph styles applied
• No character styles applied
• Switched font to Minion Pro
• Removed tabs
• Created newline (after "test") with space selected (see turqoise color)

Seeing i can enter newlines, i guess this means it's a paragraph thing right?

I'm happy to help. And it's always good to learn more about the tools you work with — that's how we work better with what we've got, even if what we learn is not immediately needed to solve issues at hand.

Because I'm not only a teacher at all this stuff, I'm also a student. I learn a lot here too.

Another thing it might be is Paragraph Shading

Format paragraphs in Adobe InDesign

And this can be set to non-printing - hence why you do not see it in other preview modes.

As above

In your preferences there are settings to highlight where things are being pushed or pulled too much in the compostion

You can see that there are highlighted areas for text, Keep Violations, H&J and so on (h&j being hyphenation and justifcation, why they haven't spelled that out is beyond me, they didn't do Custom T/K - anyway)

So in short, it's just highlighting to show you if something is off kilter, but if you're happy with how it looks then continue on.

https://indesignsecrets.com/why-am-i-seeing-yellow-highlighting-on-my-text.php

My suspicion is that those lines may "violate" minimum settings for word/character spacing by compressing the space between characters/underlining inside of preset spacing minimums. I'm guessing that you typed in the underline characters due to the variation in indents for the second "column" of your highlighted area.

It's probably not an issue for you, since as you say it seems to work fine for you. One way to check would be by trying tab leaders instead of manually typing the underlines into the text and see if the affected type is still highlighted. You can find out more on this here:

Set tabs and indents in Adobe InDesign

Setting tab leaders can help speed layout of forms in a whole lot of ways, but as you've shown it's not the only way to get the results you want.

Hope this helps,

Randy