I am currently using a dark theme which renders the Verve background black. The text starts out white but as soon as focus is lost it turns black. The issue seems to be the line, gtk_widget_modify_text (verve->input, GTK_STATE_NORMAL, &style->text[GTK_STATE_SELECTED]); in verve-plugin.c (function verve_plugin_focus_timeout_reset); though the default style has the correct font, the default style that Verve gets reset to after focus loss does not. (Also, as a side note, most of the styling functions in use seem to be deprecated.)
Possible Solution: Remove the modify_bg and modify_text lines. It seems that without the modify_base line the plugin's style will not change on blur (i.e. it will retain the blue border that appears on focus and the cursor caret will remain present) resulting in it appearing to be focused even when it isn't. The modify_base line fixes this by removing the border and cursor while the modify_bg and modify_text lines don't appear to be doing anything aside from inadvertently turning white text black.