I regularly save and freeze my cum for later, and yes, mine too gets a slight yellow tint once it's thawed. It's pretty much unavoidable. I think it's because of oxidation as it's exposed to the air. Same principle when a cut apple turns brown when exposed to the air. Not really a huge problem, just a visual change.
When I freeze my cum, the technique I use, which I find works the best, is I cum directly into plastic zip lock baggies, and I keep as much air out of the bag as possible, and get it into the freezer as quickly as possible. Also, I keep the frozen chunk of cum as flat as possible, and I don't ever put more than 10 loads per baggie. The reason for this is so that the thawing process is quicker. Cum degrades quickly the longer it spends sitting out in liquid state, so I want to make the thawing time as quick as possible, and a huge chunk of cum takes a long time to thaw. With these thin "cumsicles", I submerge the sealed baggies in lukewarm water, and the whole batch takes less than 5 minutes to thaw. Frozen cum can never have the same exact texture/color/taste of fresh cum, but I found that by using this method, it's as close as you're possibly gonna get. Once it's thawed, you have a very brief period where it's still slightly thick, assuming you got it into the freezer as quickly as possible after adding it to the baggie.
Here's a couple photos to show my freezing method. This is what I've got saved so far.
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