Writing data to specific cell in a table

Your method for finding the address of a cell is fine for formulas with an Excel worksheet. But let's take advantage of VBA features to simplify this.

When you select an item from a combobox, you can refer to the ListIndex property, rather than taking the value of the combobox and looking it up in another list.

ListIndex is 0 for the 1st element so you have to add 1.

For your grid, let's assume the data (not the headings, just the numbers) is in the range B2:E4. Let's say combobox1 has the color, combobox2 has the month. Also, ListIndex is -1 if the user hasn't selected anything.

Private Sub ButtonOK_Click()
   If ComboBox1.ListIndex < 0 Or ComboBox2.ListIndex < 0 Then
      MsgBox "You must select both month and color"
   Else
      Range("B2:E4").Cells(ComboBox1.ListIndex + 1, ComboBox2.ListIndex + 1) = TextBox1
      Hide
   End If
End Sub