After-Effects Extendscript doesn't let you use the actual color picker ships with After-Effects. Using $.colorPicker() opens the OS color picker which sucks on windows. This method adds a temporary null to a comp, then uses the "Edit Value" command in order to launch the AE color picker. Once done, the function returns the data of the new color …

GoodBoyNinjaColorPicker.jsx

function GoodBoyNinjaColorPicker(startValue){
  // find the active comp
  var crntComp = app.project.activeItem;
  if (!crntComp || !(crntComp instanceof CompItem)) {
    alert("Please open a comp first");
    return [];
  }

  // add a temp null;
  var tempLayer = crntComp.layers.addShape();
  var newColorControl = tempLayer("ADBE Effect Parade").addProperty("ADBE Color Control");
  var theColorProp = newColorControl("ADBE Color Control-0001");

  // set the value given by the function arguments
  if (startValue && startValue.length == 3) {
    theColorProp.setValue(startValue);
  }

  // prepare to execute
  var editValueID = 2240 // or app.findMenuCommandId("Edit Value...");
  theColorProp.selected = true;
  app.executeCommand(editValueID);

  // harvest the result
  var result = theColorProp.value;

  // remove the null
  if (tempLayer) {
    tempLayer.remove();
  }

  return result;
}

// launch the true color picker with a white color
alert(GoodBoyNinjaColorPicker([1,1,1]));