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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.

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 newNull = crntComp.layers.addNull(); var newColorControl = newNull("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 (newNull) { newNull.remove(); } return result;}// launch the true color picker with a white coloralert(GoodBoyNinjaColorPicker([1,1,1]));