Conditional Formatting blank cells -VBA - excel

Question

I need to highlight a cell in column B if it is less than value in column F. For example if cell B2 is 10 and F2 is 20, B2 should be red. However in column B there are blank cells i do not want these highlighted. For example B6 is blank but F6 is 10. In my code B6 become red as well.
Also how would i highlight a cell in the same row that is already highlighted. For example, if B2 is highlighted, highlight F2.
My code is below:
Sub threecf()
Dim rg As Range
Dim cond1 As FormatCondition, cond2 As FormatCondition
Set rg = Range("B2", Range("B2").End(xlDown))
'clear any existing conditional formatting
rg.FormatConditions.Delete
'define the rule for each conditional format
Set cond1 = rg.FormatConditions.Add(xlCellValue, xlLess, "=f2")
Set cond2 = rg.FormatConditions.Add(xlCellValue, xlEqual, "=isempty(f2)")
'define the format applied for each conditional format
With cond1
.Interior.Color = vbRed
.Font.Color = vbWhite
End With
With cond2
.Interior.Color = vbWhite
.Font.Color = vbWhite
End With
End Sub

Answer 1

As mentioned in my comment, use formulas. No need to use VBA
Easiest Way (Recommended Way)
I recommend this way because it takes into account new rows that are being added.
Select Col B
Select Home Tab | Conditional formatting | New Rule | Use a formula to determine which cells to format
Enter the formula =AND(B1<F1,B1<>"")
Select Format | Fill Tab
Set Fill color to red :)
Customized Way
Manually select cells B2 to last row in col B
Select Home Tab | Conditional formatting | New Rule | Use a formula to determine which cells to format
Enter the formula =AND(B2<F2,B2<>"")
Select Format | Fill Tab
Set Fill color to red :)
VBA Way
If you still want VBA then try this
Sub Sample()
Dim ws As Worksheet
Dim lRow As Long
'~~> Change as applicable
Set ws = Sheet1
With ws
lRow = .Range("B" & .Rows.Count).End(xlUp).Row
With .Range("B2:B" & lRow)
.FormatConditions.Add Type:=xlExpression, Formula1:="=AND(B2<F2,B2<>"""")"
.FormatConditions(.FormatConditions.Count).SetFirstPriority
With .FormatConditions(1).Interior
.PatternColorIndex = xlAutomatic
.Color = 255
.TintAndShade = 0
End With
.FormatConditions(1).StopIfTrue = False
End With
End With
End Sub

Answer 2

Go to conditional formatting --> New Rule --> Use a formula to determine which cells to format --> Paste This: =IF(AND(B2<F2,B2<>"") = TRUE,1,0)
For the F column: =IF(AND(F2>B2,F2<>"") = TRUE,1,0)

Answer 3

If you want a VBA solution, try it without conditional formatting:
Sub StackOverflow()
Dim x As Long
With ThisWorkbook.Sheets("Stack")
For x = 1 To .Cells.Find("*", SearchOrder:=xlByRows, LookIn:=xlValues, SearchDirection:=xlPrevious).Row
If .Cells(x, 2).Value <> "" And .Cells(x, 2).Value < .Cells(x, 6).Value Then
.Cells(x, 2).Interior.Color = vbRed
.Cells(x, 6).Interior.Color = vbRed
.Cells(x, 2).Font.Color = vbWhite
.Cells(x, 6).Font.Color = vbWhite
Else
.Cells(x, 2).Interior.Pattern = xlNone
.Cells(x, 6).Interior.Pattern = xlNone
.Cells(x, 2).Font.Color = vbBlack
.Cells(x, 6).Font.Color = vbBlack
End If
Next x
End With
End Sub
Adapt the code to your needs (change the macro name, spreadsheet address and colors if you want).