I used nuevasync to synchronize my google calendar with my iPhone.
Several months ago, google launched its own sync service, named google sync. well, it’s already got almost all the function of nuevasync, including multi-calendars, two-ways-sync and it is much faster than nuevasync. But i don’t like it because of its stupid color system . You cannot change the color of those calendars unless you pay the money (use MobileMe).

BUT i found a solution finally, specifically for jailbreake iPhone:

I found another way to do this, just playing around like you did. Copy calendar.sqlitedb from the /private/var/mobile/Library/Calendar directory on your iPhone to your computer, and make a backup of it (recommended). Open it with SQLite Dabase Editor (http://sourceforge.net/projects/sqlitebrowser/) and go to the second tab, “Browse Data”. Under “Table”, choose “Calendar”. This will give you a list of all of the calendars on your phone. Each row is a different calendar. There are three columns - color_r, color_g, and color_b. Set these to whatever you want for your RGB colors for each calendar. (It is not limited to five colors). Save the file and copy it back to your phone.

更新：用此软件还能解决中文tag显示为乱码的问题

Problem:
iTune and iPhone 3G provide a fancy function - Showcasing your album artwork when you listen to your music. But it is quite tedious to add the artwork by yourself.

Solution:
Tag & Rename is a music files tag editor -- easily handles all popular digital audio formats, as it said on its website.
It supports a lot of formats. With it, you can edit your mp3 tags, including artist, title, album name, etc. And you can load the album artworks from amazon.com.

Step by Step guild:

1. Download the software from Tag & Rename.
2. Install it and open the folder contains your music, select mp3
3. Press "F4" to batch rename your mp3 or Press "Shift+F4" to get the correct tags from your mp3's name.
4. Press "F11" to synchronize your mp3 tag between ID3v2 and ID3v1 ( you may switch the tags view between ID3v2 and ID3v1with "Alt+1" and "Alt +2").
5. Press "F10" to get Tags info from amazon.com including Cover Artworks.
6. Please be noted that  Tag & Rename is not a freeware. You have to do sth if you want to use it after one month...