a search for "reasons for variegated plants" brought lots of hits.

Begin with wikipedida
http://en.wikipedia.org/wiki/Variegation

move on to Union County College
http://faculty.ucc.edu/biology-ombrello/POW/variegated_plants.htm

And here's something from UCLA
http://www.botgard.ucla.edu/html/botanytextbooks/generalbotany/shootfeatures/generalstructure/leafcolor/variegation.html

and lots, lots more

Here is a link that might be useful: from UCLA

As the previous post indicates, there are a lot of reasons for variegation and I seriously doubt you can attribute defined percentages to specific causes. It may be safe to say that the largest number of variegations occur as the result of a genetic imbalance or abnormality - chimeras. Some variegation does arise as the result of a virus - patterned tulips are a classic example as are most variegated forms of abutilon - but I think you'd be hard pressed to assign a defined percentage to this type of variegation. Not all mottled, speckled or streaked plants are afflicted with a virus. Only DNA testing can confirm the source of this type of variegation.

Relatively few variegated cultivars are variegated due to viruses. The examples above are exceptions, not "the rule". Often, plants affected by viruses will show considerably less vigor or may even show noticeable decline.

Variegation patterns due to viruses are distinct from many other variegation patterns. Virus-caused variegation exhibits blotchy patterns (except in the case of hostas, where all variegation is virus-caused and should be eliminated from the garden immediately).

"Variegation patterns due to viruses are distinct from many other variegation patterns. Virus-caused variegation exhibits blotchy patterns (except in the case of hostas, where all variegation is virus-caused and should be eliminated from the garden immediately)."
Are these viruses that bother other plants?

Toronado,
The hosta thing was just for Ken (he's a big hosta grower). But, to answer your question, generally viruses have fairly specific hosts.

hey brandon.. spot on.. lol ...

that was actually funny ..

regarding virus in hosta ... see the link

and while you are there.. take some time to go to the hosta library HOME page ... go figure on all that ...

ken

Here is a link that might be useful: link

Gotta tell me when we're just picking on Ken!!!!

:)