WHY DO THE BULBS IN MY GARDEN GROW IN DIFFERENT COLOURS EACH YEAR?

They are almost certainly not the same plants. While some plants – hydrangeas, for example – may well change flower colour when grown in soils of different acidity levels, it’s unlikely that the soil conditions will have changed markedly around a bulb from one year to the next. Very rarely a genetic mutation might occur that could result in the loss of a particular pigment, changing flower colour, but it is much more likely that seedlings or other previously non-flowering bulbs have come up in more or less the same spot.