OO Writer | Toolbar | Formatting
The Background Fill icon does not remember the last color selected.
When you click on the glyph, it activates the drop-down color palette.
The Text Color icon and the Highlight Color icon both remember the last color selected.
If you click on either icon, you get the "current color" indicated in the bar underneath the glyph (without having to visit the color palette).
Resolution: make the Background Fill toolbar icon show the "current color" and make that color happen on the page without having to visit the color palette.
[ I hope this is helpful. I am a huge fan of OpenOffice. User since 2010. ]