Changing all blue color numbers/texts to black color in cells...

Try this. the blue color font index in your sample file is 12611584

Sub Test()
Dim ws As Worksheet
Dim i As Integer
Dim cell As Range

For i = 1 To Sheets.Count
    Worksheets(i).Select
        For Each cell In Cells.SpecialCells(xlCellTypeConstants)
            If cell.Font.Color = 12611584 Then
                cell.Font.Color = vbBlack
            End If
        Next cell
        
        For Each cell In Cells.SpecialCells(xlCellTypeFormulas)
            If cell.Font.Color = 12611584 Then
                cell.Font.Color = vbBlack
            End If
        Next cell
Next i

End Sub