OEM sproket covers are boring.....

[Agemax]

You could use a similar system to that used in some yo-yo's. A centrifugal switch in a fully enclosed case with button cell batteries.

but that would mean bolting it to the clutch and a; looking silly, and b; maybe unbalancing the mojo of the clutch.
good suggestion but i am looking into other options

[bonanzadave]

Ive thought about doing red mesh behind it but red would clash with the rest of the planned paint work. Gold or brass would look the best IMO but Im going to leave it open for the time being until the paint work is done and I can get a better visual. More than likely, its going to get brass.

Red LED ? That would look spiffy at night.