Two more, since I just can't stop tinkering with this data:

LinearGradientImage across all individual sweater colors, in order:

ImageResize[
 LinearGradientImage[
  Normal@SortBy[ResourceData["Mister Rogers' Sweater Colors"], 
     "Date"][All, "SweaterColor"]], {800, 200}]

First blend all colors for each year, then apply LinearGradientImage to the blended colors:

ImageResize[
 LinearGradientImage[
  Normal@(Blend /@ 
     Values@GroupBy[
        ResourceData[
         "Mister Rogers' Sweater Colors"], #Date["Year"] &][[All, All,
         "SweaterColor"]])], {800, 200}]