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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.

For bird of paradise, regardless of type, a balanced fertilizer is preferable. This can be purchased at nearly any home and garden center, like Lowes, Home Depot, Walmart, etc. in your area. Look for something that has a balanced NPK number (like 8-8-8, 10-10-10, or 20-20-20).

You leave out one important piece of information - is your plant outdoors or in a pot? Outdoors they're incredibly tough. Almost impossible to underwater them, so about the only problem is too much water. Indoors, the most likely problem is also overwatering, although it is possible that a potted plant receiving too little water would also show the same symptoms. If you test the soil (in a pot) with a moisture meter, it should read about 1/2 way between dry and moist, with the meter inserted to the bottom of the pot, before it's watered again. When watering, there should be a runoff from the drainage holes.
Another couple of things to check are for possible damage of some kind which might cause the plant to fall over, and insects, which most likely would be mealy bugs. Here are a couple of articles that might have a bearing on your plant: https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-an-exotic-flower-like-none-other.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/mealybugs-control.htm

There can be several things that can cause faded blooms on plants. The most common is that the flowers fade in color as the bloom gets older. But, if your plant started out with faded color, it may be that it is lacking fertilizer or is seeing sunlight much more intense than it is use to. Once in a great while, if a single bloom comes out without color, this is simply a sport or a mutation and is not an issue.

Prune out any dead or weak growth. For hard pruning cut back all branches. I would not cut it back by more than 1/3 a year. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-pruning.htm