Color Artifacts in Fourier Transformed Image
Some things you should keep in mind:


Your image is real, keep your DFT Symmetric.
Numerical issues might cause that after the Inverse DFT imaginary parts are lefts.
Use either abs or real to get rid of them.
One should understand what it means to "Zero" out by mask DFT values.
It is not the "Ideal LPF". It causes Ringing / Halos due to Gibbs Phenomenon. One should use better designed LPF.


I hope it helps.