Well, we had 2 different color roses on the same bush this spring, but I think I figured it out. I missed pruning a sport from below (is that what it's called? not a rosarian) & it was sending up roses from the original rootstock. That's my theory, anyway.

The rose I can see. The 'sucker' is from the root stock, which is grafted to the flower stock.

they don't change colors completely from one season to the next but can branch-sport with different colors or get flecks/stripes of darker colors in the individual flowers. gumpo white often has flowers with flecks and stripes of dark pink to red in them.
my 'george l. taber' occasionally throws out a solid purple-flowered branch. if i recall, that is where it originated -as a sport of purple formosa or similar.
of the encores, 'autumn twist' will occasionally have two different solid colors of flowers as well as those with flecks.

Jeff,
That 'sporting' is really common on the Geo. L.Taber - it was very common to find branches sporting solid purple blooms, or even some that were predominantly the normal pink with purple stripes, or one purple petal, etc. Mrs. G.G.Gerbering is, if I recall correctly, a white sport of GLT.
I've lost track of the historical info, but I was always under the impression that Formosa was a sport of Pride of Mobile(or maybe it was the other way around).

hi lucky,
yes, i knew i had seen this question before on gardenweb and found an old post about the cultivars mentioned above.
mrs. g is a white sport of taber and taber is a sport of a purple, not unlike formosa, called 'omurasaki'.
the post is linked below.
interesting how this happens to give us some beautiful new varieties. one reference i read claims that the sporting is the result of bud damage on the original plant.

Here is a link that might be useful: azalea sports

The picture in that link looks exactly like my azalea, before and after.

Thanks for all the help. I think I'll just go out and get another white azalea, just for balance.

My azalea changed colour too, last year I had one white azalea and one purple azalea,this year the white one is wearing Pink. Last year the buds were white and the Blooms were also white. This year the buds started out a dark pink and as the blooms open they turn a lighter pink, and when they fully open they are a pale pink. it’ll be interesting to see if the purple one stays purple

We may have the same, Aututmn Twists. But some of the plants are mixes, and some are all purple. This might help explain. https://www.youtube.com/watch?v=ejS3oYJapcg

I have one that is light pink with dark pink flowers mixed in this year. One flower got confused and is half and half!

I had dark pink mixed in this year with my light pink. One flower got confused and is half and half.

My white one also flowered pink this year!

Azaleas changing colors... I'm so glad I found this set of comments, gets me a few clues. My white azalea bush came with the house and according to the neighbors is at minimum 15 years old. All blooms pure white for 3 years but this year one blossom is sporting a dark pink stripe.

Pretty. i had quite a few dark pink mixed in with my light pink bush this year. a few half and half as well.

I was given a white azalea as a gift by my granddaughter. last season, this season it is a pink. not a pink person. i had the same trouble with a hydrangea & was told sulphur would fix it. Going to give it a go on the azalea