Why do some Havanese change colour as they mature?

There are many different genes which control colour in Havanese (at least 10 and quite likely more).  Some of the genes regulate colour, some determine pattern and markings and others are modifier genes.  The modifier genes are the ones which cause many of the changes you may see. Some cause the colour to lighten or soften or to develop in certain ways. Some affect colour in a very significant way and others affect it more subtly.  Some genes affect only light colours, other affect only dark colours and some affect both. Oftentimes, there is little way to know if these genes are in play until you see the effects of them.
 
- Light coloured dogs change the least.  White stays white.
- On dogs with colour plus white, the white may either stay pure white or may sometimes develop flecks of colour throughout. This is called ticking.
- Sable is one of the most changeable colours in Havanese. There are two main reasons for this. Dark tipping once cut off generally does not grow back, so a puppy that starts dark may appear much lighter as an adult. As well the base coat may soften as the dog matures. Just these two factors can lead to an adult dog that bears little resemblance to what he looked like as a puppy. A Sable dog generally will retain some dark tipping at least in the ears and tail where the dark hairs are most concentrated.
- Some dogs lighten and then darken again as they mature.
- Others develop colour banding in their coats.
- Many colours soften over time.
 
One thing is for sure. Havanese colours are always interesting and intriguing.