@SuppressWarnings("unused")
	private void addFunctionHighlight(VTMarkupType markupType, String text, int cursorTextOffset,
			HashMap<VTMarkupType, VTMarkupItem> typeMap, ArrayList<Highlight> highlightList) {
		VTMarkupItem markupItem = typeMap.get(markupType);
		if (markupItem != null) {
			Stringable value =
				(isSource || markupItem.canUnapply()) ? markupItem.getSourceValue()
						: markupItem.getOriginalDestinationValue();
			if (value != null) {
				String displayString = value.getDisplayString();
				int startIndex = text.indexOf(displayString);
				if (startIndex >= 0) {
					int endIndex = startIndex + displayString.length() - 1;
					Color highlightColor =
						getMarkupBackgroundColor(cursorTextOffset, markupItem, startIndex,
							endIndex);
					Highlight highlight = new Highlight(startIndex, endIndex, highlightColor);
					highlightList.add(highlight);
				}
			}
		}
	}
Creates a darker shade of the color passed-in, based on the given amount.

algorithm: 1) grab individual rgb elements
           2) multiply each by a factor.
           
           ie: int newRed = (int)(oldRed * 0.85);

@param color the color to shade
@param amount number between 0..1 (the smaller the number, the darker the shade)
@return the new color
Ghidra/Features/VersionTracking/src/main/java/ghidra/feature/vt/gui/duallisting/VTDualListingHighlightProvider.java