Highlight active rows while ignoring any cell with a fill color

I have conditional formatting and VBA to highlight active rows on a spreadsheet.

We use it on the next row to the one we're briefing because it changes the fill on the entire row.

Is there a way to ignore any cell that already has a fill color?

Current Conditional Formatting

=CELL("row")=ROW()

Current VBA

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Application.CutCopyMode = False Then
    Application.Calculate
End If
End Sub

I've only been able to highlight the entire active row.

You need a way to exclude cells which have any existing fill from passing the Conditional Formatting "highlight row" rule.

To do that you can add this UDF to a regular module:

'Return True if the calling cell has no fill
'  Functions called from a CF rule formula have the
'  calling cell as `Application.Caller`
Function NoFill() As Boolean
    NoFill = (Application.Caller.Interior.ColorIndex = xlNone)
End Function

and add that to your CF rule formulas for row and column highlighting:

=AND(ROW()=CELL("row"),NoFill())
=AND(COLUMN()=CELL("col"),NoFill())

Example showing using the down arrow to step through rows (only using row highlighting CF rule):

Updated to add:

In a "real life" application using a larger range, this turned out to be unworkably slow - recalculating the worksheet to update the CF means every cell in the range with those rules has to be evaluated.

So here is something more scalable - it starts by deleting any pre-existing row/column-highlighting rules on the sheet, and then add rules only for the selected row/column, and only for cells with no fill:

In the worksheet module:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
    If Application.CutCopyMode = False Then
       AddCFRules Target.Cells(1) 'in case of >1 cell selected
    End If
End Sub

In a regular module:

Option Explicit

'called from Selection_change event handler
Sub AddCFRules(c As Range)
    Const NUM_ROWS As Long = 1000 'adjust to suit...
    Const NUM_COLS As Long = 500   'adjust to suit...
    With c.Worksheet
        RemoveRowColumnRules .Cells '#### changed to only delete some CF rules###
        DoEvents
        AddCFRule .Cells(c.row, 1).Resize(1, NUM_COLS)     'row highlight
        AddCFRule .Cells(1, c.Column).Resize(NUM_ROWS, 1)  'column highlight
        .Calculate
    End With
End Sub

'add a rule to hilight a range
Sub AddCFRule(rng As Range)
   Dim fc As FormatCondition, cfRange As Range
    Set cfRange = UnFilledRange(rng)    'only unfilled cells
    If Not cfRange Is Nothing Then      'any unfilled cells?
        With cfRange.FormatConditions.Add(Type:=xlExpression, Formula1:="=TRUE")
            .StopIfTrue = False
            With .Interior
                .PatternColorIndex = xlAutomatic
                .Color = vbYellow
                .TintAndShade = 0
            End With
        End With
    End If
End Sub

'scan all cells in `rng` and return a Range with only unfilled cells
Function UnFilledRange(rng As Range) As Range
    Dim c As Range
    For Each c In rng
        With c.Interior
            If (.ColorIndex = xlNone Or .Color = vbWhite) Then
                If UnFilledRange Is Nothing Then
                    Set UnFilledRange = c 'first cell
                Else
                    Set UnFilledRange = Application.Union(UnFilledRange, c) 'all other cells
                End If
            End If
        End With
    Next c
End Function

'Delete any formula-based CF rules with "=TRUE" as the formula
'Allows other rules to be used on the sheet
Sub RemoveRowColumnRules(rng As Range)
    Dim i As Long, fc As Object
    'Debug.Print "checking CF rules:" & rng.FormatConditions.Count
    For i = rng.FormatConditions.Count To 1 Step -1
        Set fc = rng.FormatConditions(i)
        If fc.Type = xlExpression Then
            If fc.Formula1 = "=TRUE" Then fc.Delete
        End If
    Next i
End Sub

Having to exclude filled cells from the CF range is a bit awkward: ideally we'd add the same formula used in the first iteration, but for some reason it doesn't seem possible to create a CF rule in VBA using this formula. eg:

With someRange.FormatConditions.Add( _
            Type:=xlExpression, _
            Formula1:="=AND(ROW()=CELL(""row""),NoFill())")

fails with no error, and code execution stops at that point.
Using Formula1:="=ROW()=CELL(""row"")" works as expected.

Later: I found that if you use a global variable eg

Dim skip as Boolean

and use that a flag to exit the UDF referenced by a CF formula:

Function NoFill() As Boolean
    If skip Then Exit Function
    NoFill = (Application.Caller.Interior.ColorIndex = xlNone)
End Function

then you can set skip to True when applying the CF rule via VBA, and it will successfully set up the rule without breaking. When done adding the rule(s), set skip to False.