DataGridView Custom CheckBox Column

I lately had a need to a checkbox column in a DataGridView, but with custom images (plus, minus and a question mark). DataGridViewCheckBoxColumn images cannot be changed, so I had two options: Customize the OnPaint event, or recreate a new DataGridViewColumn.

I decided to go on the second option. I created a DataGridViewThreeStateCheckBoxColumn class(I prefer long names on abbreviations):

public class DataGridViewThreeStateCheckBoxColumn : DataGridViewImageColumn
{
    public DataGridViewThreeStateCheckBoxColumn(ImageList images, bool isThreeState)
    {
        this.CellTemplate = new DataGridViewThreeStateCheckBoxCell(images, isThreeState, true);
    }
}

And a DataGridViewThreeStateCheckBoxCell class:

public enum eState {Unknown = 0, Positive = 1, Negative = 2}
public class DataGridViewThreeStateCheckBoxCell : DataGridViewImageCell
{       
    private Dictionary StateToImage { get; set; }

    private bool IsReadOnly { get; set; }

    private eState cellState;      
    public eState CellState
    {
        get
        {
            return cellState;
        }
        set
        {
            cellState = value;
            this.Value = StateToImage[cellState];
        }
    }

    public DataGridViewThreeStateCheckBoxCell()
    {
    }

    public DataGridViewThreeStateCheckBoxCell(ImageList images, bool isThreeState, bool isReadOnly)
    {
        StateToImage = new Dictionary { { eState.Unknown, images.Images["question-mark"] }, { eState.Positive, images.Images["plus"] } };
        if(isThreeState)
            StateToImage[eState.Negative] = images.Images["minus"];
        CellState = eState.Unknown;
        IsReadOnly = isReadOnly;
    }

    protected override void OnMouseClick(DataGridViewCellMouseEventArgs e)
    {
        if (IsReadOnly)
            return;

        // toggle the cell state
        CellState = ((eState)(((int)CellState + 1) % StateToImage.Count));

        base.OnMouseClick(e);
    }
}

In may case I also need a way to notify the parent on state changes, to update a database. I did this by creating an event that the parent was able to register to.