A peak rectangle in the mixer strip is ruled by "gtk_bright_indicator". In the previous commit I mixed up this item with "meterbridge label" & "meterbridge peakindicator". This commit changes "gtk_bright_indicator" from white to red and returns "meterbridge label" & "meterbridge peakindicator" state to primordial. So now the peak rectangle in the mixer strip will be red when a sound peak has a place.