Macro not working when I "Call" it from another macro, but does work when I select it individually - excel

Question

I have a formatting macro below:
Sub Colour_whole_sheet()
Dim lastRow As Long
Dim lastColumn As Long
lastRow = Range("A1").End(xlDown).Row
lastColumn = Range("A3").End(xlToRight).Column
'Colour alternate rows purple / white
For Each cell In Range(Cells(1, 1), Cells(lastRow, lastColumn))
If cell.Row Mod 2 = 1 Then
cell.Interior.Color = RGB(242, 230, 255)
Else
cell.Interior.Color = RGB(255, 255, 255)
End If
Next cell
End Sub
It doesn't run when I call it from another macro, which is just:
Sub Run_macros()
[A bunch of other subs]
Call Colour_whole_sheet
[A bunch of other subs]
End Sub
It doesn't come up with an error - it just doesn't do anything. But when I select it specifically on its own, from View > Macros > View Macros > Run, it works fine.
Do you know why this might be?
EDIT:
Sub Colour_whole_sheet()
Dim ws As Worksheet
Set ws = ThisWorkbook.Worksheets("Calendar")
Dim lastRow As Long
Dim lastColumn As Long
lastRow = ws.Range("A1").End(xlDown).Row
lastColumn = ws.Range("A3").End(xlToRight).Column
'Colour alternate rows purple / white
For Each cell In ws.Range(ws.Cells(1, 1), ws.Cells(lastRow, lastColumn))
If cell.Row Mod 2 = 1 Then
cell.Interior.Color = RGB(242, 230, 255)
Else
cell.Interior.Color = RGB(255, 255, 255)
End If
Next cell
End Sub

Answer 1

you might be after this revision of your code
Sub Colour_whole_sheet(Optional sht As Variant)
If IsMissing(sht) Then Set sht = ActiveSheet ' if no argument is passed assume ActiveSheet
Dim lastRow As Long
Dim lastColumn As Long
Dim i As Long
With sht ' reference passed/assumed sheet object
lastRow = .Cells(.Rows.Count, 1).End(xlUp).Row ' best way to get a column last used cell row index
lastColumn = .Cells(3, .Columns.Count).End(xlToLeft).Column ' best way to get a row last used cell column index
'Colour alternate rows purple / white
With .Range("A1", Cells(lastRow, lastColumn)) ' reference all your range
.Interior.Color = vbWhite ' color it white
For i = 1 To .Rows.Count Step 2 ' loop through referenced range uneven rows
.Rows(i).Interior.Color = RGB(242, 230, 255) ' color them with purple
Next
End With
End With
End Sub
as you can see:
it always references some sheet(be it passed through sub argument or be it the active one)
it doesn't loop through all cells, but just through uneven rows

Answer 2

Here Range("A1") is not specified in which worksheet this range is. Always specify a worksheet for all your Range(), Cells(), Rows() and Columns() objects.
Otherwise it is very likely that your code runs on the wrong worksheet. Note that this is applicable to all your macros (not just this one). Check if you have specified a worksheet everywhere, or your code might randomly work or fail.
Dim ws As Worksheet
Set ws = ThisWorkbook.Worksheets("Sheet1") 'your sheet name here
Then adjust the following lines:
lastRow = ws.Range("A1").End(xlDown).Row
lastColumn = ws.Range("A3").End(xlToRight).Column
For Each cell In ws.Range(ws.Cells(1, 1), ws.Cells(lastRow, lastColumn))
Also note that you can format an Excel table to get rows alternated colored.
Additional notes:
The method you used is not reliable in finding the last used row/column. Better do it the other way round. Start in the very last row and go xlUp.
lastRow = ws.Cells(ws.Rows.Count, "A").End(xlUp).Row 'Last used row
lastColumn = ws.Cells(3, ws.Columns.Count).End(xlToLeft).Column 'last used column in row 3
Also you don't need to go through all cells. Looping throug rows would do.
Dim i As Long
For i = 1 To lastRow
If i Mod 2 = 1 Then
ws.Rows(i).Interior.Color = RGB(242, 230, 255)
Else
ws.Rows(i)..Interior.Color = RGB(255, 255, 255)
End If
Next i
or if you don't want to color the whole row but only up to the last used column
ws.Cells(i, lastColumn).Interior.Color
Note that coloring each row on on its own can slow down a lot if there are many rows. Therefore I suggest to collect all even/uneven rows in a reference and color it at once.
lastRow = ws.Cells(ws.Rows.Count, "A").End(xlUp).Row 'Last used row
lastColumn = ws.Cells(3, ws.Columns.Count).End(xlToLeft).Column 'last used
Dim EvenRows As Range
Dim OddRows As Range
Dim i As Long
For i = 1 To lastRow
If i Mod 2 = 1 Then
If OddRows Is Nothing Then
Set OddRows = ws.Rows(i)
Else
Set OddRows = Union(OddROws, ws.Rows(i))
End If
Else
If EvenRows Is Nothing Then
Set EvenRows = ws.Rows(i)
Else
Set EvenRows = Union(EvenRows, ws.Rows(i))
End If
End If
Next i
If Not OddRows Is Nothing Then OddRows.Interior.Color = RGB(242, 230, 255)
If Not EvenRows Is Nothing Then EvenRows.Interior.Color = RGB(255, 255, 255)