Why the green in Libre Office Math (0-128-0) is not the same as in Libre Office Writer (0-255-0)?
It is not easy to have the same color to the Math formula and text around it. Or is it?
LibreOffice Math is in fact MathML, only that not all features of MathML are supported. In LibreOffice Math only the named HTML colors of Basic HTML data types are supported. Those names are different from the color names in Writer. But you can easily add the HTML colors to your personal color palette using Tools > Options > LibreOffice > Colors.
The color names in the palette have only local relevance, because for texts not the color names, but the number values are stored in the file. When a text document is opened, the number values are mapped to the local names. The local names are localized, so in an English UI you will see “Purple” and in a German UI you will see “Purpur” for the same color.
That is the reason, why “green” in Math is not the same as “green” in Writer.