I had that happen to a Poinsettia before...it was red when I purchased it and when it rebloomed the following year it was White!! From the research I did I found out that sometimes because they breed these in so many colors the gene pool gets mixed and sometimes they carry more than one color in the plant and can change colors? It way beyond my comprehension,lol... I have a bougainvillae that I'm trying to grow as a Bonsai...Here's a picture of it last January when it was blooming...

Propagate your own root stock the easy way with 'Pot Over Pan' To obtaining sturdy bougainvillea roots, take a young potted plant and stand it over an empty upturned pot, larger and shallow. For ease of description, growers call this the 'Pot Over Pan' method. This pot upturned pot should preferably be shallow - say not more than 3 or 4in. in depth, with a base wider than the upper pot - that is why it can also be called a 'pan'. It must have large holes (carefully made with a chisel or drill) at its base. The upturned pot should then be placed directly over the earth. Or filled with earth before upturning. Here is how it is done. Pot as you normally would for a young plant, but do not close up the holes at the bottom with broken bricks. Leave them relatively open, but plugged with a thin layer of dried grass or coconut husk. Then position the potted plant over the upturned pot in . such a way that the holes of both pots are aligned. Where you place this setup is important. You should choose a patch of ground in your garden which is quiet yet sunny and where there is little disturbance from gardeners or grasscutters. Loosen the soil in the ground, and better still, add soil mix and work it into the ground. Soon roots will appear, unrestrained, from the bottom of the upper pot and reach through the large holes of the upturned pot, heading straight down into the earth - now rich with soil mix - in search of water and nutrients. Gradually the roots will have firmly anchored into the earth, but harvest only when they have developed to a diameter of 3/16-1/4 in. or more. Do this by gently cutting off the roots from under the base of the pot holding the young plant, making sure you do not damage the roots. (When this is done, you will notice that the leaves of the plant will start to droop due to the shock. All you need do to revive it is to water the plant and transfer it to a shady spot, and soon it will resume its normal healthy self.) Next, lift up the upturned pot carefully. You will see that the roots, quite likely mixed with soil, curled around inside, and with their bottom ends firmly anchored to the earth. Cut them off at the base unless you can gently but firmly pull them out from the earth. Finally remove the soil from the harvested roots, wash them thoroughly, and plant them as root stock. The usual method of root grafting can be practised. If upturned pot was filled with dirt, then cut dirt into 3 parts and trans plant each root set in its pot. Align holes between the two pots to allow roots to reach the Cover holes of pot with thin layer of dried grass or coconut husk. After some months, roots reach downwards through large holes inuptumed pot. Loosen existing soil in the ground, and better still, add soil mix. Cut off roots from plants. Remove roots by digging gently so as not to damage them. Transplant.

Thank you!! We're in the Bay Area; although we had a couple decent rains this winter., we're still in a drought. I've been watching our neighbor's healthy bougainvillea, and it also dropped its flowers a lot later than ours did, but it's south facing, so I just realized it got sun all winter while ours didn't. I'm more worried about the sparser leaves and the soft trunk. Good to know about the braiding, although there's not much I can do about it now. Yes, socalgal -- I've been wracking my brain to think of what could have changed in the months since we bought the house, since it clearly *had* been a very happy plant for a long time! But I'll just give it some more time and see what it does over the next few months.

@Louisa More questions to add to what I asked already: 4) Where do you live and what is your plant zone? 5) Describe your weather pattern throughout the year. 6) Applying some common sense, does the soil in which these plants live feel dry or moist between waterings, going down about 10 inches? You want to have someone do the percolation test and I gave you a link to a thread that talks about how to do it. This is very very important for your case. We have no idea if your soil is wet or dry, and whether it drains fast or slow. Bougainvillea wants to live in dry soil and then be drenched once every week or two. They want the water to drain fast. You probably don't have those conditions. Also, if you did not figure it out by now, the photo of your variant makes clear that it is the wrong plant for that small wall location unless you are willing to maybe put up a trellis and very actively prune it.