In the last year there has been a significant increase in the number of dilute coloured dogs being sold in the UK. The majority are being bred by French Bulldog and English Bulldog extreme-colour breeders, many using dogs imported from the U.S.A. or Eastern Europe, presumably as the market for both has passed the peak and they see an opportunity to make significant money from 'rare' or 'coloured' dachshunds.

The blue colour is a dilute of the black and tan; Isabella (also known as lilac in other breeds) is the dilute of the chocolate colour. The gene that causes the dilute colours can also cause an issue in some dogs called colour dilution alopecia (CDA), where the hair shaft is thin and weak, meaning it can drop out of the follicle and cause baldness. Because the coat is thinner than normal, the skin can also be more susceptible to infection and sunburn, which in turn may cause cancer.

Read more here.