Auto Color whole column when found text "Sunday"

The code below works well also. However, I got 2 problems here.
First, I manage to find the word " Sunday", then color the cell below that Sunday. However, I need Excel auto find out Sunday and color that particular columns for me, for example, Sunday found and color start from cell(L55) below that Sunday up to more cells(L59), Range("L55:L59").
Second, I only manage to find first Sunday, I wish the system keep find and keep color untill it found that rows blank, so I using this code.
'Encountered blank cell in row 2, terminate search
If Len(Cells(2, LColumn)) = 0 Then
MsgBox "No matching date was found."
Exit Sub

I attached the excel files with sample, I really hope someone can help, these problems delay me 2 months d. Thanks alot !

<script type="text/javascript">
Sub AutoColor()
 
    Dim LDay As String
    Dim LColumn As Integer
    Dim LFound As Boolean
    
    On Error GoTo Err_Execute
    
    'Retrieve date value to search for
    LDay = Sheets("Rolling Plan").Range("B4").Value
    
    Sheets("Plan").Select
    
    'Start at column B
    LColumn = 2
    LFound = False
    
    While LFound = False
    
        'Encountered blank cell in row 2, terminate search
        If Len(Cells(2, LColumn)) = 0 Then
            MsgBox "No matching date was found."
            Exit Sub
        
        'Found match in row 2
        ElseIf Cells(2, LColumn) = LDay Then
             
            Sheets("Plan").Select
            Cells(3, LColumn).Select
            
       With Selection.Interior
        .Pattern = xlSolid
        .PatternColorIndex = xlAutomatic
        .Color = 40000
        .TintAndShade = 0
        .PatternTintAndShade = 0

    End With

            LFound = True
            MsgBox "The data has been successfully copied."
            
        'Continue searching
        Else
            LColumn = LColumn + 1
        End If
            
    Wend
    
    On Error GoTo 0
    
    Exit Sub
    
Err_Execute:
    MsgBox "An error occurred."
    
End Sub
</script>

You don't need VBA to do this. Conditional Formatting will work

See this

http://excel-it.com/excel_conditional_formatting.htm

Select a cell & using the Conditional Format dialog in the formula is box type

=B$2="Sunday"

Then use th Format painter to copy the Format to the other cells.

Can't see why you need this because you have fixed the text as the day of week, it won't change so you could just colour the cells manually

I cannot see the point in using VBA when an inbuilt Excel Function is available, Conditional Formatting would be quicke 7 more efficient than code

Looking at your exampleit is totally different to the first, the days are added by formulas. Why waste time adding a workbook that is different?

You still can do this with Conditional formatting, whereas your VBA will fail because Sunday is formatting not the actual cell's value.

You can change the Formula in B3 to =Text(b2,"dddd") then use this formula for CF

=B$3="Sunday"

Alternately, use this formula

=WEEKDAY(B$2,1)=1