Filter thread on G9 housing?

I've been looking at getting an Ikelite G9 housing, one reason being that I thought I could attach a color filter to remove the violet lighting from my UV dive light when I take pictures of fluorescence. I haven't yet been able to figure out how the filters are attached to the Ikelite housing, and calling the Ikelite office was fruitless.

Can someone out there tell me what thread or other form of attachment is used to attach color filters to the Ikelite G9 housing? Is the only way to get a threaded port to install the flat port 9305.92, which appears to have a 67mm thread?

We offer two different types of color correcting filters for our housing for the Canon G9. Both are held by rubber shrouds that press onto the front of the lens port. The #6441.41 U/R Pro red filter replaces reds and oranges in tropical blue water settings. The #6441.81 green water filter provides more natural tones in freshwater settings.

Both the standard housing port and the optional #9305.92 short port feature 67mm threaded fronts.

Regards,
Jean / Ikelite
IKELITE Underwater Systems