I assume you are talking about this product. According to the MSDS, the product contains 100% "Disodium salt of ethylenediaminetetraacetic acid, dehydrate,Disodium sulfate" which is also known as EDTA which is a metal chelating agent. You are correct that this is not an algaecide.
The instructions for Yellow Out have you first raise the pH above 8.0 (which could result in some cloudiness or scaling, depending on other water parameters). You then add 2 pounds of Yellow Out per 15,000 gallons. You then add Cal-Hypo or liquid chlorine (chlorinating liquid or bleach) to add about 10 ppm FC. You then circulate for 24 hours. Finally, you add another 10 ppm FC of chlorine.
Their process is patented here where interestingly the patent is essentially using chlorine plus ammonia to form chloramine which is the primary decolorizing agent. I am going to guess, on the basis of this patent, that EDTA breaks down under higher levels of chlorine in alkaline (higher pH) conditions. I am guessing that they are using EDTA rather than ammonium sulfate in their product since they don't have to label the ingredients and it makes things less obvious.
So basically this product just forms chloramine to kill the algae and then you add more chlorine to get rid of the chloramine.
Of course, you could just shock with chlorine alone instead, but may need higher levels of chlorine due to higher CYA in the water. Using ammonia or bromine gets around the CYA issue by forming monochloramine or bromine that are not affected by CYA. It is not an approach promoted on this forum.
As for your yellow/mustard algae, if that is what it is (rather than pollen), you need to shock at a high level and then maintain a higher FC than you are currently doing. 2 ppm FC with 50 ppm CYA is not sufficient. Ben's Best Guess CYA Chart requires a MINIMUM FC of 3 ppm with 50 ppm CYA. Unless you completely get rid of the yellow/mustard algae, even higher FC levels may need to be maintained, but certainly 2 ppm is not high enough. If the problem is pollen and not algae, then a skimmer sock is the way to go (or a pool cover).