Hello,

Thank you for your question and your helpful photographs.
Too much water may lead to nutrient deficiencies and cause yellowing of older leaves. Specifically, there may be a nitrogen deficiency and application of appropriate fertilizer may help. Most garden centers can assist you with this.

Attached is an article from Colorado State University. Please see the section titled "similar symptoms", and the paragraph on nitrogen deficiency.
http://www.cmg.colostate.edu/Gardennotes/223.pdf

A soil test is another way to determine what the level of nutrients in the area of this plant.
I have attached a link to CSU's soil lab as well.  http://www.soiltestinglab.colostate.edu/

Thank you and please let us know if we can assist further.