Linoleum stain help

Try rubbing a paste of baking soda and water on it. Let sit for a while and then scrub..

Sounds like the glue is coming up from underneath. I don't think anything on the surface will help. Talk to your installer. He may have used the wrong adhesive.

Judith, we had a similar issue here. We had a 6X8 area rug under our dining room table and it left a bad 6X8 dark brown stain on our off white tile pattern linoleum. Have 3 cats that has a problem with area rugs in the dining room..... they are persistently marking them. Didn't have the funds to put down new linoleum throughout the whole kitchen and dining room , so I opted to find a complimentary color of stick on linoleum tiles to cover that area. That was over 3 years ago and it's worked out perfectly. The tiles actually looks like a designer floor and meant to be that way. Looks like an inset on purpose. Perhaps you could try that and extend the area a tad so it doesn't look like a couple foot patch. No way I found to remove the stain we had had tried everything. The tile was the last resort.

http://www.howtocleanstuff.net/how-to-remove-yellow-stains-on-linoleum-flooring/

a baking soda paste should do the trick! good luck!