Q.yellow bird of paradise
We have several orange and white bird of paradise plants but recently saw some yellow flowers here in San Diego. Is this a different plant or is there something different with the soil conditions that cause the color change?

Most likely the yellow flowers - assuming you're still looking at a bird-of-paradise - are from a sport, either a new plant that has grown from seed, or even a branch that for some unknown reason starts putting out flowers or foliage slightly different from the main plant.