Interface PointFigureColumn

Per-bar colour override, honoured by every Family-A renderer: candles and OHLC bars take it on body, border and wick together, histogram and column on the bar, and line, step, area and the HLC-area close line split their stroke into runs at the bars where it changes. Baseline is the exception, its stroke is already split by the above/below-base rule. A MACD histogram is four colours by momentum, and a conditional study is two. Neither is expressible with one colour for the whole series.