Linoleum starts to yellow as it ages and or covered up eith a rubber backed rug. There's nothing you can do, sorry.
I tried a baking soda paste. Let is sit overnite but nothing. Afraid once it yellows that is it.
That is likely rust from nails underneath. Yeah you could use CLR and rub your arm off every 3 weeks, but the Only way to get rust out permanently is to remove the source of the rust. Namely the Nails in your subfloor or floorboards under the Linoleum (which should have been instead Galvanized Steel Screws) need to remove and replace with Galvanized Screws. You can do this! Several ways.
The easiest with sheet linoleum? Not terribly hard: 5 to 7 minutes per Rusty Nail and 6 easy steps.
1. Use A Small Hole Saw, 3/4 inch, without the Center Bit, to remove a Very Tiny Area of the Linoleum enough to get at the rusty nails. File very gently the edges smooth of that cutout. If it cracks or breaks, remember you have more matching linoleum beneath your fridge or stove.
2. Remove the nails that are rusty (by prying these up with a Sharp Flathead Screwdriver and a Board as the Fulcrum) And clean the area with ajax or pine sol.
3. Screw in a Galvanized Steel Screw of a Size equivalent to a 12D nail into the Spot where the Rusty Nail was.
4. Use Glue or Putty to put the Linoleum you cut out back where it was.
5. Heat the Linoleum with a Blow Dryer so it expands a bit and the Putty or glue is more smooth on the edges.
6. Move on to do same to the Next.
With Tile it is entirely different as you just pull up the tile and put down 1 of the excess tile that you always have leftover.
Worst comes to worst: you just get some Other Colored Tile and create a Dot Pattern Mosaic.
Huh?! Rusty nails?!
Try pouring ammonia and letting set. You will need to have the area ventilated for fumes.
Try one cup of lemon scented ammonia, a few squirts of Dawn dish liquid to one gallon hot water. If this does not work it's just naturally yellowed.