There are a number of factors that can cause your Iris to stop blooming. Planting in too much shade, Iris should have at least half a days sun. Overfeeding with animal manure or blood and bone, also the opposite, not feeding them at all. Planting too deep, Iris should not be planted more than 2-3cm below the soils surface. Planting too high, the rhizomes have been exposed to too much sun. Mulching of any kind. This acts as shade and also keeps the moisture around the rhizomes which can cause them to rot. Over/under watering. And if they are overcrowded, Iris need to be thinned/transplanted every 3 years otherwise the clump gets too overgrown and the plants can’t access nutrients and water readily.

There is no possible way that an Iris can change colour unless it has sported (a mutation that rarely ever happens). Usually what happens is that two varieties are being grown to close together and they have grown into one-another. This causes the more prolific and dominant variety to suffocate the other variety which stops it from blooming. Using weedkillers like Roundup can cause flowers to turn white but it also changes the flower shape itself, you can usually tell when weedkiller is the culprit.

Ideally they should be planted immediately after lifting. However, if this isn’t possible they can be left in a cool dry place for months. Ensure that they are kept DRY though otherwise they will rot.