Please describe the problem:
When you compose a mail message in html format, if you set text color of a line
to be different from the default one, then, after you press enter key to start a
new line, the new line's text will get the default color, but the color combo
still previews the former customized color. 

Steps to reproduce:
1. Open Evolution, choose New->Mail message.
2. Choose Format->HTML, locate the cursor in the first line and set text color
to be different from the default through composer's color combo. Then color
combo will preview customized color.
3. Press several characters, which have customized color. Then, press enter key
to start a new line.
4. Press another several characters. They get default color, but the combo still
previews customized color.


Actual results:
The combo preview color isn't consistent with the new line's actual text color.

Expected results:
When the new line's texts get default color, the combo's preview should also
refresh properly.

Does this happen every time?
yes

Other information:
It will confuse users.