Datamap - Change color depending on value

I came across a datamap example here and trying to edit it. I need to change the state color depending on the value, ranging from dark blue to light blue.

At the moment,

fills: {
            'lightBlue': '#cc4731',
            'justBlue': '#306596',
            'deepBlue': '#667faf',
            'mediumBlue': '#a9c0de',
            'deepBlue': '#ca5e5b',              
            'defaultFill': '#eddc4e'
        }

And the data has,

data: {
            AZ: {
                    fillKey: 'lightBlue',
                    userVisits: 5
                },
            CO: {
                    fillKey: 'justBlue',
                    userVisits: 5
                },
            DE: {
                    fillKey: 'deepBlue',
                    userVisits: 32
                },
            ....
}

But is there to generate shades of blue depending on the userVisits?

I don't think there is a an option to put logic in the fillkey selection. I'd recommend processing the data to assign a fillkey before giving it to Datamaps. I made a codepen to demonstrate. Also, the "fills" data has duplicate keys and hex values that do not match the color described.

var stateData = {
        AZ: {
                userVisits: 5
            },
        CO: {
                userVisits: 15
            },
        DE: {
                userVisits: 32
            }
    }

function addFillKey(mapData){
  for (var mapDatum in mapData){
        var userVisits = mapData[mapDatum].userVisits;
        if(userVisits < 10){
            mapData[mapDatum].fillKey = "lightBlue"
        }else if(userVisits < 20){
            mapData[mapDatum].fillKey = "justBlue"
        }else{
            mapData[mapDatum].fillKey = "mediumBlue"
        }
    }
}

addFillKey(stateData);

var map = new Datamap({
  element: document.getElementById('container'),
  scope: 'usa',
  fills: {
    'lightBlue': '#cc4731',
    'justBlue': '#306596',
    'deepBlue': '#667faf',
    'mediumBlue': '#a9c0de',
    'deepBlue': '#ca5e5b',              
    'defaultFill': '#eddc4e'
  },
  data: stateData

});