An interface controller (13), situated between a graphics controller (6) and a frame buffer memory array (8) in a color video display system is operable in a read-modify-write mode, and is configured to detect a select transparency color in whole or in part and to respond by selectively changing the color binary data for the corresponding pixel in a frame buffer. Drawing modes are implemented by logically combining pixel color binary data in accordance with a defined truth table so as to allow the pixel color data representing a new image to interact in a defined manner based upon color with the data in a previously defined image. The binary data in the frame buffer (8) is acted upon in a read-modify-write sequence whereby the various logic operations analyze the source (foreground) pixel data, the destination (background) pixel data, in the context of control signals, to define the pixel color data written into the frame buffer (8) as the color representation for that pixel position.
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