Isn't it green?
Then it might be the error warning symbol. If you select the cell, you'll get an exclamation mark and a drop down telling you what
the "error" is (like referring to currently empty cells)

--
Kind regards,

Niek Otten
Microsoft MVP - Excel

"Bill (St. Jude)" wrote in message
...
| What is the significance of the little blue triangle in the top left corner
| of an Excel 2007 cell?