Rear Fog Light. . . . .

[Graham-P]

Does the lens have to be red, or can it be clear(ish) with a red bulb?

[Steve_D]

It only has to produce red light and satisfy the inspector that the light intensity is comparable with an EC standard lamp.
My Dakar front lights failed as they were LED and he considered them too bright and that they had a blue tint.

Steve