Date Picker issue - Monday - first weekday

Question

In the USA, the first day of the week is Sunday, but in many European countries the first day is considered Monday (see the attached captures). I was able to make it show the calendar accordingly, but there is an issue regarding the colors.

Sunday - first day of the week

Monday - first day of the week

The days of the month changed accordingly, but the colors of each CommandButton remain the same (see the light-yellow colored area). The portion of code which controls these colors is found in

Sub Build_Calendar()

If Format(DateAdd("d", (i - Weekday((CB_Mth.Value) & "/1/" & (CB_Yr.Value)), vbMonday), _
        ((CB_Mth.Value) & "/1/" & (CB_Yr.Value))), "mmmm") = ((CB_Mth.Value)) Then
            If Controls("D" & (i)).BackColor <> &H80000016 Then Controls("D" & (i)).BackColor = &H80000018  '&H80000010
            Controls("D" & (i)).Font.Bold = True
        If Format(DateAdd("d", (i - Weekday((CB_Mth.Value) & "/1/" & (CB_Yr.Value)), vbMonday), _
            ((CB_Mth.Value) & "/1/" & (CB_Yr.Value))), "m/d/yy") = Format(ThisDay, "m/d/yy") Then Controls("D" & (i)).SetFocus
        Else
            If Controls("D" & (i)).BackColor <> &H80000016 Then Controls("D" & (i)).BackColor = &H8000000F
            Controls("D" & (i)).Font.Bold = False
        End If

Does it know anyone in which way should I modify this code in order to have proper colors of the CommandButtons?

Thank you,

Dan