Color Isolation Controls are required to evaluate the accuracy of a display's conversion of non-RGB signals to RGB, and to correct any conversion errors via the display's color decoder controls. Where physical isolation isn't possible, an electronic means is needed in order to view each color channel separately.
To evaluate and adjust a display’s color decoder, it is necessary to view a color bar test pattern and, in turn, evaluate the blue, red and green color channels in isolation. This is ideally achieved by physically or electronically blocking two of the three primary color sources.
For example, to evaluate the accuracy of a color decoder for the red channel, the blue and green channels must be temporarily blocked, so that the effectiveness of red decoding can be easily observed.
For digital displays, color isolation must be achieved through electronic means, as there typically is no workable method for physically obstructing an individual color channel. On the other hand, this is easily accomplished with a front- or rear-projection CRT display by blocking the light coming from the lens for each CRT.
Where neither electronic or physical isolation is possible, a third option exists -- use of color filters that can be held up to one's eyes. The most commonly available color gel filters, bundled with many home theater test discs, are designed to match the SMPTE-C primary color standards, as defined by the Society of Motion Picture and Television Engineers.
Unfortunately, very few consumer displays strictly adhere to SMPTE-C primary color standards, and as a result filters typically do not perfectly match the display’s primary colors, making the filters less than 100% effective.