Why are my yellow roses red?

I have a yellow rose bush in my back yard,but this year the roses are all red instead of yellow. Can anybody tell me why???

Why are my yellow roses red?
Your rose may be a grafted (as opposed to own-root) rose and the rootstock is taking over - this is not a good thing! If the flowers are very deep red, semi-double blooms, your rootstock is Dr. Huey. You can try removing the rootstock where it is starting to grow, but you will probably need to replace your rose.
Reply:they catch a cold,..... i gess
Reply:do u have a red one close by? red is dominant and will usually change other roses to red! watch out! it could have been grafted to a red rose root system too... never know!