looping from one column to the next

[Brad Zenner]

it's a simple macro that i've created, because I'm still a newbie at all of
this.

basically, the macro goes down each cell in a column, and if the cell's
value is greater than 300, then it puts in a background color into the cell.
the macro stops when the cell has nothing in it (the end of the column). I'd
like it to jump to the next column and repeat the macro, but not sure how to
do it. Here's what I've got so far:

Sub testcolors()
ActiveCell.Select
Do Until ActiveCell = ""
If ActiveCell = "" Then End
ActiveCell.Select
If ActiveCell > 300 Then
With Selection.Interior
.ColorIndex = 6
.Pattern = xlSolid
.PatternColorIndex = xlAutomatic
End With
End If
ActiveCell.Offset(1,0).Activate
Loop
End Sub

Any help is greatly appreciated. Thanks.
Brad