Iron stains and hard water stains, if they are bad enough you can see "lines" where the stain starts and stops, that is negative, considered a dirty pot. Subtle staining, and the subtle change in color over time is considered good. So if you are getting the "lines" outlining the edge of the iron stain, like a coffee stain on a napkin or tablecloth, that is too heavy, and an attempt to get the stain to fade is appropriate - the vinegar for hard water, oxalic acid for iron stains.
Otherwise, what I can see from the photo I think the pot is just fine, I'd leave it alone. I have a yellow YiXing pot, that has been used for 15 years, it has gone from pale yellow to a warm medium dark earth colored yellow, that could pass for a brown color. Its now a nice subtle color, no longer a bold distracting color.