I had that idea once but half way does not work well since half way between UTC 3 and UTC 4 is UTC 3 30 but this has nothing to do with DST So even if half way is used one needs to alter another parameter apart from hue The model is HSV that leaves S and V for DST markation On the Indiana map I wanted to have different colors for two hues the map only uses UTC 6 hue 0 red and UTC 5 hue 60 yellow see commons File UTC TZ hue4map USA IN svg