Not all colors sync between the iPad/iPhone

Week Calendar 3.1 and Week Calendar HD 1.1 support syncing custom colors assigned to an event between Week Calendar on different devices. This way, you can set an event to red on your iPhone and see it as red on your iPad as well.

Enable / Disable

You can enable this feature in Settings > General > Events & Syncing > Synchronize Colors.

Notes

To be able to do this technically, Week Calendar needs to be able to store the color somewhere in the event that will get synced to your other device(s). The only place available for this is the notes field of an appointment.
When you enable Color Syncing, Week Calendar will store the assigned custom color as a small piece of text in the notes of an event. This piece of text will be automatically hidden inside Week Calendar, but will show up in other applications that don't support color syncing.

Technical Limitations

Due to technical limitations, the following is not yet possible: