From my experience,
I donít think there is. Bettas tend to change colour due to Tempeture, Water, Paremeters ( not sure thatís how to spell it) etc. I found it is because basically the consistions their in. For example a Betta fish in poor conditions will show poor colouration, meaning markings will not stand out very much. Where as a Betta in good conditions will show very bright colouration and depending on the conditions your Betta that should determine his colouration and markings. If you could post photos maybe it would help a bit for us to look at the environment he/she is in. If you are not able to, would you be able to explain what conditions he is in? If you are not able to do that as well, from my experience, no, there is probaly no way you could help your Betta to keep his present colouration and markings. However, there might be a way to match water conditions if you ask for his current owners water peremeters, tempeture etc. Anyway, back to the point, like I said from my experience there is no way to keep the same colouration of a Betta.