When I am out of fresh tomatoe, I use tomatoe puree and I observe that my Garlic turns Green/Blue in final receips. I seriuosly got scared and threw out garlic. One day when I saw on America's Test Kitchen and came to know this:

"Working on a pasta sauce recipe for an upcoming issue, test cook Erika Bruce noticed that fresh garlic cloves sometimes take on an odd blue-green shade when cooked with acid (tomatoes, in this case).Under acidic conditions, isoallin, a compound found in garlic, breaks down and reacts with amino acids to produce a blue-green color. Visually, the difference between garlic cooked with and without acid can be dramatic, but a quick taste of the green garlic proved that the color doesn't affect flavor."

Hope it Helps!