I got a pair of lights from vanline, red in colour, brake/park in red, but the centre when reverse polarised gave a yellow/amber flash. Read that again, the whole lens IS RED, but the centre changes to yellow. Drawback - they are smaller dia than the C4's, never tried them against the 78, I'll see if I can find them in the garage. Vanline are on ...... not Airds rd, but off it on ..........
Oh nearly forgot, naturally since they change colour, they are LED.