You'll have to draw it yourself. Here is what
this MSDN page says about the topic:
You can customize most of the TreeView colors by setting color properties,
but the selection highlight color is not available as a property.
However, that page also shows you how to custom draw nodes yourself, and it even shows specifically how to change the color of the highlighted node. Note that my use of TreeView is very limited... I found this information with Google... Google is your friend. Not sure if you just got unlucky this time, but I suggest you Google a bit first before asking questions here. It only took me 5 minutes to find that information (actually, more like 30 seconds to find it and 5 minutes to review it). Imagine how much time you could save if you learn how to use Google.