Why did Kaoru's hair color change? In the very start of the first episode, Kaoru had Dark blue hair. But after that, her hair color changed to blonde. Why did Kaoru dye her hair?  Does it mean something like a start of a new chapter of her life? What is the significance of this in the story?

During the Marriage/Honeymoon:


At home (and the rest of the episodes):
When they got married, Kaoru's hair was black.
After a while, Kaoru dyed her hair blonde.

In the web comic version, chapter 6 has the story explaining the reason why Kaoru dyed her hair blonde:



Title: Sadako


1st frame: (With impersonations of Sadako) I—am—Sa—da—ko—
2nd frame: Hajime: Uwah~~~ Sadako-tan so moe~~~ I want to lick you all over~~~
3rd frame: (Kaoru is angry)
4th frame: Hajime: Oh? You dyed your hair? (Kaoru is sulking)


I think, Kaoru did a (light) cosplay of Sadako to get Hajime's attention, but he called her Sadako instead of Kaoru, so she got angry and dyed her hair blonde.