There doesn’t seem to be any control in any of the menus or toolbars to change text colour.
Traditional way: Add the appropriate toolbar choosing menu View - Toolbars - Text Formatting.

New way: Press Ctrl+F5 (the same that menu View - Sidebar), click on the Properties button, and unfold Character.

Tested with LibreOffice 6.4.7.2 (x86); OS: Windows 6.1.
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Thanks I think that’s done it. Not used to an office program where the formatting functions aren’t already there on the visible toolbars.