How to apply color function to my financial indicator?

Question

My goal is to make a figure like this picture in a financial indicator,

I want to plot “a colored” financial indicator below a trading chart.

I prepared financial data and data of my indicator:

spy = FinancialData["SPY", "OHLCV", {{2020, 12, 1}, {2020, 12, 10}}];
indicatorData = {{{2020,12,1},1}, {{2020,12,2},2}, {{2020,12,3},3}, 
{{2020,12,4},-1}, {{2020,12,7},-2}, {{2020,12,8},-3}, {{2020,12,9},1}, 
{{2020, 12, 10}, 3}};
myIndicator = 
FinancialIndicator[TimeSeries[indicatorData] &, "LineStyle" -> Blue,
"IndexLine" -> 0];

The plot of the data is

TradingChart[spy, {myIndicator}]

I want to use Hue and Filling to fill the indicator with color, depending on "colorData" which is a set of dates and Hue values,

colorData = {{{2020,12,1}, [email protected]}, {{2020,12,2}, [email protected]}, 
{{2020,12,3}, Hue@0}, {{2020,12,4}, [email protected]}, {{2020,12,7}, [email protected]}, 
{{2020,12,8}, [email protected]}, {{2020,12, 9},Hue@0}, {{2020,12,10}, Hue@0}};

I need to fill the region between my indicator and x-axis by using Filling.

Although I guess Hue and Filling are keys to my question, any idea would be appreciated.

Answer 1

If you are willing to give up interactive display of legends, you can post-process Setting @ TradingChart[...] to get a graphics object with desired filling style:

myIndicator = FinancialIndicator[TimeSeries[indicatorData] &,
  "LineStyle" -> Blue, "IndexLine" -> 0]; 

Setting @ TradingChart[spy, {myIndicator}, ImageSize -> Large] /.  
 subplot : Line[MapIndexed[N@{#2[[1]], #} &, indicatorData[[All, -1]]]] :> 
  {First @ 
   ListLinePlot[First @ subplot, Filling -> 0, 
          FillingStyle -> Automatic, 
          ColorFunction -> (Blend[colorData[[All, 2]], #] &)], 
   subplot}