The standardization of high beam indicators started some time in the eighties and changed to a blue light resembling a headlamp in order to reduce confusion with warning lamps.
Various auto manufacturers and vehicle models changed over at different times
It was actually the mid '70's, SlantSixDan just answered this one in another thread somewhere, cited FMVSS I believe '77 model year. ALL vehicles had to comply w/the
std. for that model year, or sell the car in another country. Yes, it is to not confuse a warning lamp You may have been ignoring, w/the hi beam indicator alerting You that
you are blinding oncoming traffic.