[Histonet] Yellow Walls in the Lab

[Smith Wanda]

Good Morning Netters,
As much as I hate to admit this...the walls in my lab where the tissue processors, embedding center, UPS for the embedding center, and microtomes are, they are turning yellow.  It has been happening gradually, however now when the histotechs wipe the counters each day, the paper towel is yellow.  It almost looks like nicotine tar, but they assure me they are not smoking in there in the mornings!!!
My lab is 3 years old and they designed it with adequate ventilation to remove fumes, but I'm at a loss on this one.  Please help!!!!!
Wanda