public class ComboBoxData : BaseViewModel
    {
        private Brush _labelsColor;
        private string _textConst;

        public Brush LabelsColor
        {
            get => _labelsColor;
            private set => Set(ref _labelsColor, value);
        }

        public string TextConst
        {
            get => _textConst;
            private set => Set(ref _textConst, value);
        }

        public ComboBoxData(Brush color, string text)
        {
            LabelsColor = color;
            TextConst = text;
        }
    }


//===========================================

public class EditTaskWindowViewModel : BaseViewModel
    {
        private List<ComboBoxData> _cbData;
        private ComboBoxData _cbSolo;

        public ComboBoxData cbSolo
        {
            get => _cbSolo;
            set => Set(ref _cbSolo, value);
        }

        public List<ComboBoxData> CBData
        {
            get => _cbData;
            set => Set(ref _cbData, value);
        }

        public EditTaskWindowViewModel()
        {
            CBData = new List<ComboBoxData>();
            InitializecbData(0, 148, 204, "Will definitely happen"); //new Color(#0094cc)
            InitializecbData(0, 178, 72, "Need to do"); //Brushes(#00b248)
            InitializecbData(249, 168, 37, "It is desirable to do"); //Brushes(#f9a825)
        }

        private void InitializecbData(byte r, byte g, byte b, string text)
        {
            Color tmpColor = new Color();
            tmpColor.G = g;
            tmpColor.R = r;
            tmpColor.B = b;
            SolidColorBrush tmpSolidBrush = new SolidColorBrush(tmpColor);
            Brush tmpBrush = tmpSolidBrush;

            ComboBoxData cbd = new ComboBoxData(tmpBrush, text);
            CBData.Add(cbd);
        }
    }

//===========================================

<ComboBox Height="28" Margin="50,48,25,124" ItemsSource="{Binding CBData}" SelectedItem="{Binding cbSolo}">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Rectangle Height="10" Width="10" Margin="3, 0">
                            <Rectangle.Fill>
                                <SolidColorBrush Color="{Binding LabelsColor}"/>
                            </Rectangle.Fill>
                        </Rectangle>
                        <TextBlock Text="{Binding TextConst}"></TextBlock>
                    </StackPanel>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>