On macOS (but not on Windows or Linux), in versions 7.1.x and 7.2.x of LibreOffice, a bug in Base causes the Memo (LONGVARCHAR) field type to have a dark background, so the contents are not visible. Other field type [date, number, TEXT (VARCHAR), and so on] have a normal white background. When clicked, the black fields turn white and I can type into them, but when I click or Tab to another field, they return to black. When I use a form to enter data, the form fields are normal, but the results in the database itself have the black field background. The database otherwise works as it should.
This behaviour has been reported as Bug 140854. The workaround is to use an older version of LibreOffice, such as 7.0.x, where the bug does not occur. You can find a link to version 7.0.6 near the bottom of the download page.
Fortunately, it is easy to install more than one version of LibreOffice on macOS, so you don’t have to completely give up the latest version if you want to use it for other components. Simply rename the existing version to something else; I usually change “LibreOffice” to “LibreOffice721” or similar. Then install a second version as usual by double-clicking the downloaded DMG file. Both versions will share the same user profile, so it’s easy to switch among them. Note: You can set up separate user profiles (for example, for testing purposes), but that’s beyond the scope of this article; see this wiki page if you want to go there.