white roses now pink

[betsy garden]

my white rose bush is now producing flowers with a pinkness to then instead of the pure white they used to be.
How do I get them back to the pure white?

[Clanad]

My first guess is that you have a hybridized rose... either a tea or a floribunda. These are produced by grafting two different roses together. You can tell by a grafting "knob" near the bottom of the plant just above where it emerges from the soil. In one case a "sucker" has emerged from below the graft and is producing a rose from the original stock... in which case, cut it off below the ground level. Secondly, tea roses (and some floribundas) can and do revert tothe original color if, as you indicate, there's not a lot of difference in the colors now being produced.
There's very little that can produce color change in the way of feeding. Some fungus diseases, especially botrytis can cause reddishness on new blooms, but is spotty and not consistent in tone. Best of luck!