How-to use function stored in another workbook

I have a worksheet that has cells coloured via conditional formatting. I need to count the various cells by colour - after much searching & experimenting I've got the two functions below to work with the following formula :-
=CountCellsByColor(range, color code)

Problem is that I need to do this in many different workbooks. All my other macros are housed in a central workbook so that I don't have to do much more than open the "storage" workbook, the file to be worked on & then run the appropriate macro.

My question is how do I use the two functions below via that central workbook ??
What changes do I need to make to the functions (if any) & how would I "execute" the formula via the macro or would it be as simple as Range("A1").formula="=CountCellsByColor(range, color code)" ??

Many thanks

Function GetCellColor(xlRange As Range)
    Dim indRow, indColumn As Long
    Dim arResults()
 
    Application.Volatile
 
    If xlRange Is Nothing Then
        Set xlRange = Application.ThisCell
    End If
 
    If xlRange.Count > 1 Then
      ReDim arResults(1 To xlRange.Rows.Count, 1 To xlRange.Columns.Count)
       For indRow = 1 To xlRange.Rows.Count
         For indColumn = 1 To xlRange.Columns.Count
           arResults(indRow, indColumn) = xlRange(indRow, indColumn).Interior.Color
         Next
       Next
     GetCellColor = arResults
    Else
     GetCellColor = xlRange.Interior.Color
    End If
End Function
 
 
Function CountCellsByColor(rData As Range, cellRefColor As Range) As Long
    Dim indRefColor As Long
    Dim cellCurrent As Range
    Dim cntRes As Long
 
    Application.Volatile
    cntRes = 0
    indRefColor = cellRefColor.Cells(1, 1).Interior.Color
    For Each cellCurrent In rData
        If indRefColor = cellCurrent.Interior.Color Then
            cntRes = cntRes + 1
        End If
    Next cellCurrent
 
    CountCellsByColor = cntRes
End Function

Thanks Alan - didn't know about those files.

Issue is that, unfortunately, I'm not always the person running the routines hence looking at ways so that anyone can run the macros which incorporate the functions.