That stuff is the "Krausen", its mostly foam from dead yeast and unusable proteins that gets stuck to the side of the carboy. Surely you've seen it if this is your 3rd batch. The Krausen is normal, let it be.
But, I have never seen that yellow colour before.
What yeast did you use?
What did you use inside your airlock? Sanitzer? Idophor? They might be the culprit if the krausen crept up inside the airlock, as is common with one gallon batches, and may have caused the off color. Sanitizer solutions like Starsan are fine, but I wouldn't consume it if you filled the air lock with an idophor solution.
Does it have an off smell? Or does it smell like the yeast you put in?