I regularly use correction gels on my Sigma 15/30mm zoom. There is no filter thread because the front element protrudes so far forward, but on the back of the lens is a clip that was designed to accept 25mm square gel filters. I bought a job lot from pale yellow right through to deep orange and cut the correct size for my needs. I only wish there was a red available as well.
They work exceedingly well and even if they get light scratches there is absolutely no degradation of the image.