Well i had added a comment to a cell and then changed the cell background to red because the number in the cell was a negative number and now there is not visible indication that there is a comment in the cell.
I can confirm this :)
Laurent Godard committed a patch related to this issue.
It has been pushed to "master":
draw white border around note marks for fdo#81032
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.
I think drawing a white border around it would make it look bad on non white cell backgrounds that arent red. Maybe a good choice is to have it as the inverted color of the background color when the background isnt white or a light color.