In a SMPTE color bar image, the top two-thirds of the television picture contain seven vertical bars of 75% intensity. In order from left to right, the colors are white, yellow, cyan, green, magenta, red, and blue. This sequence runs through all seven possible combinations that use at least one of the three basic color components of green, red, and blue, with blue cycling on and off between every bar, red cycling on and off every two bars, and green on for the leftmost four bars and off for the rightmost three. Because green contributes the largest share of luminance, followed by red, then blue, this sequence of bars thus appears on a waveform monitor in luminance mode as a downward staircase from left to right. The graticule of a vectorscope is etched with boxes showing the permissible regions where the traces from these seven bars are supposed to fall if the signal is properly adjusted.