<p></p>
<p>My question is for clarification about what OP means by "appropriate marker".  It's not clear what qualifies as a "marker" to OP, except <em>maybe</em> that it "display HEX and RGB colors".</p>
<p>How important is the "highlighting" part?  Maybe not at all, if the primary purpose is to show the color that's represented.  But if highlighting is the primary purpose, numbers, including hex values, are already highlighted, and the secondary purpose of showing colors may not be possible.</p>
<p>But if showing the color is the primary purpose, a tooltip could accomplish that without changing any Scintilla or Geany styles.  The plugin would just need to extract the hex code and screen location.  Then it could use GTK to display the color independently of scintilla when the mouse cursor is the right position.</p>

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