are you trying to highlight parts of cell and not other parts (not possible)
or are you saying in the list/column you are checking there are cells that are not numeric? this is possible:
under conditional formatting select custom formula then
=ISNUMBER(A1)*(A1>10)
would highlight A1 if it is a number AND > 10
make sure your formula is based on the upper left cell in the applied to range using $ to 'lock' the row/column if needed and do not use $ when you want the reference to be relative.
