Can the duct tape be any colour?

You can change the text color to black by dragging your finger all the way down to the bottom right corner of the screen. Dragging your finger from here to...

Rest assured that your phone will operate just fine without active service from a carrier, leaving it as a WiFi-only device.

You can color it, but it is not required. Remember, you can draw whatever you would like, so leaving it uncolored or colored is your choice!

You could use regular tape, but it won't work as well as florist's tape. Florist's tape is easier to work with and fits in better with the flower because it's...

No. You need to have double-sided tape to make the tape. If you don't have double-sided tape, you can buy it from craft stores, or any other kinds of stores.

Yes, you can. You can make it into decorative stickers since Washi tape is a decorative tape.

It can be regular duct tape, as long as it isn't see-through. It should be black, if possible.

Tape will not last as long as glue, especially a glue made for paper. There's no reason you can't use origami paper, though.