Conditionally Formatting Formula Results

How would I change the colour of a cell depending on the result of a formula? I cannot change the formula itself to include an IF function.

I have several cells that im using CONCATENATE on to combine them. The cells im combining do not always have data. If the CONCATENATE only returns 1 character i would like to turn it green. Conditional Formatting is not recognizing it thus far.

if A1 = 1 then green
if A1 = 2 then green
if A1 = 12345 then nothing

Attach an example workbook with the problem so we can examine your conditional formatting formulas.....

=LEN(A1)=1
format as green
assuming there aren't any spaces or other invisible characters as a result of your concat.

Select your range then in the conditional formatting reference the first cell in your range. Excel will automatically compensate with the other cells, so

=LEN(K1)=1
Glad to help