Não tem como resolver, é uma característica do vidro dela..
Alguns dizem que expondo ao ultravioleta o processo pode ser revertido. Tenho minhas dúvidas. É claro que o tom influencia na foto sim.
"The Spotmatic Group Method
Here is the method we use on the Yahoo! Spotmatic group:
How to Cure Yellowing in Takumar 50mm f1.4 lenses.
Remove both lens caps and wrap the uncapped lens, except the rear element,
in aluminum foil and then set it on a windowsill that faces towards the sun.
Prop it up with something (like a rolled-up towel) so that it tilts in order
to get the most sunlight into it. Then go away and leave it.
A mild case takes about a week to ten days on a windowsill in California.
A severe one takes about a month.
The foil serves two functions. It reflects light off the lens body and
thus reduces heat buildup that otherwise would occur due to the black
finish on the lens and this could affect the lubrication inside the lens.
And by not capping the lens before wrapping it, light makes its way from
the back of the lens and reflects back off the foil at the front of the lens,
thus attacking the yellowing again.
This "sunlight cure" method has been successfully employed by a number of
members of the Spotmatic group and many 50mm f1.4 lenses which were
thought to be useless for colour photography have now been returned to
active service with "water clear" glass.
Some others have reported good results in about three weeks using an
ultraviolet light source.
The yellowing problem affects the Model II 50mm f1.4 Super-Takumars and all
other 50mm f1.4 lens through to the K-mount series.
The older Model I 50/1.4 Super-Takumars, the 8-element ones (which can be
distinguished by the protruding element at the rear NOT having a
protective metal rim), do not turn yellow because they do not have
the radioactive element, using an additional regular optical glass element to
get higher refraction instead. The Yellowing problem also affects the later
f2 35mm lenses with 49mm filters."
http://www.orau.org/ptp/collection/consumer%20products/cameralens.htm