Is there a possibility to add colours to the WYSIWYG? Or only through HTML?

with Quill, adding 'color' to the toolbar should work

Nice it works! Is there also an option to add table support?

not in quill unfortunately, but the "tiptap" type option of the wysiwyg field does (default in twill 3). the approach we have been using to continue using quill for everything else than tables was to create a dedicated table block where we put only a tiptap wysiwyg with only the table feature enabled in the toolbar