SF_FormulaPlotter: Make trace colors work with swapped axis

When plotting text waves we plot them using the category axis feature
including swapping X and Y waves. But if we do that we also need to query
the opposite wave for the trace colors.

Bug present since e1854b0 (SF: Change average operation to support two
modes, 2023-04-05).

Packages/MIES/MIES_SweepFormula.ipf

@@ -1903,7 +1903,16 @@ static Function SF_FormulaPlotter(string graph, string formula, [DFREF dfr, vari
 				WAVE wvY = dataInGraph[l][%WAVEY]
 				trace = tracesInGraph[l]
 
-				WAVE/Z traceColor = JWN_GetNumericWaveFromWaveNote(wvY, SF_META_TRACECOLOR)
+				info = AxisInfo(win, "left")
+				isCategoryAxis = (NumberByKey("ISCAT", info) == 1)
+
+				if(isCategoryAxis)
+					WAVE traceColorHolder = wvX
+				else
+					WAVE traceColorHolder = wvY
+				endif
+
+				WAVE/Z traceColor = JWN_GetNumericWaveFromWaveNote(traceColorHolder, SF_META_TRACECOLOR)
 				if(WaveExists(traceColor))
 					ASSERT(DimSize(traceColor, ROWS) == 3, "Need 3-element wave for color specification.")
 					ModifyGraph/W=$win rgb($trace)=(traceColor[0], traceColor[1], traceColor[2])