Purple heart, and many other woods like osage, darken when exposed to light. Make a fresh cut in that purple heart, it will be very purple. As it ages, it turns darker, mellows out.
Sounds like the wood you have, the dark side was cut long ago and the bright side was recently cut.
You can finish it any way you like, I am not sure you can stop the "ageing" process. And I think it looks better "aged".