Question
I have three yellow rose bushes spread out throughout my garden.  The past 4 years (along as I have had them), they have produced beautiful yellow roses.  This year, one of the bushes is producing bright pink roses with no hint of yellow.  Can the soil composure change the color of roses or is it simply changed due to cutting?

Answer
Roses are like human beings and have blood lines. When a breeder is looking to bred a new rose they select the roses from other roses blood lines and then mix them. There are enough roses that go into making another a new rose that would fill a legal size page. What has happened to your rose is that it has sported to one of the roses in it's background. Usually though it is only one flower that sports. I wonder if you are seeing the under stock? There is a picture on my site of Dr. Huey a well used under stock. It is under climbers 2 .Have a look and see if it looks like your roses. Hope this helps.
http://www.theoldrosarian.com/