You could use comditional formatting. Select your range.
I will assume a1:a6 for the example. Under format
conditional formatting, choose "formula is" and write:

=COUNTIF($A$1:$A$6,A1)1

set your pattern or font to color your dupes
Lance
-----Original Message-----
I have a column with numbers, these numbers are unique,
is there a way to write into a formula that if a number
repetes the color of the numbers turn red.
.