Why would a flower have a common name that includes 'changing'? I am only aware of one, the changing forget-me-not (Myosotis discolor); there may be others but I cannot recall them at present. The answer is that the colour of the flowers of the changing forget-me-not change as they age and, as the flowers open in sequence up a central stem, the newly emerging ones at the top are cream, just below they are yellow, then there will be some pink ones and finally the lower ones are blue. At the bottom of the stem the early ones will be turning to seed heads. The flowers in many plants change as they open. The birds'sfoot-trefoil, for example, starts partly orange and turns yellow when fully open but to have a full sequence of three or four colours on one flower spike is unusual.
Changing forget-me-not is not that common in Dorset preferring bare patches on dry, slightly acid soil and a lot of Dorset is alkaline lime and chalk. It flowers from May until September and can be quite prolific where it does occur.