Rachelle,
Under the post 'Pistachio Mint 'Geyserland' check page #2.
What you see changing color is the "lip" of the cymbidium as opposed to the three sepals and the two petals.
Primary causes are: 1) the normal aging of the flower; 2) the loss of the white pollen cap making the flower think it has been pollinated or 3) just an insect crawling in and out of the flower also affecting pollination. In your case I suspect the second as the pollen cap is missing on your photo. Environment would only play a part if continued dry and warm or freezing temps hasten the total demise of the flowers and that would affect the whole spike.
Enjoy your plant and to gain more information, browse the other postings on this Board.
Good Luck,
CL