categories: resolution and color. In resolution modes, each pixel is addressable as either on or off. There are two colorsets available: black dots on a green background with a green border, and white dots on a black background with a white border. In color modes, each pixel uses two bits to select one of four colors, with the overall colors determined by the colorset: a green border with the colors green, yellow, red, and blue; a white border with the colors white, cyan, magenta, and orange. Resolution graphics store 8 pixels per byte and are available in 128×64, 128×96, 128×192, and 256×192 modes. Color graphics have 4 pixels per byte and are available in 64×64, 128×64, 128×96, and 128×192. The maximum size of a bitmap screen is 6144. Artifact colors The 256×192 two color graphics mode can display four colors due to a quirk in the NTSC television system. These are called composite artifact colors. In the first colorset, where green and black dots are available, alternating columns of green and black appear as a muddy green color. With the white and black colorset, the result is either orange or blue. Reversing the order of the alternating dots gives the opposite color. In effect, this mode is 128×192 with four colors: black, orange, blue, and white. On PAL televisions, instead of solid orange and blue, artifacts appear as vertical stripes of green and peach with soft edges and a width of almost four pixels. On a CoCo 3 with an analog RGB monitor, the black and white dot patterns do not artifact. The bit patterns that represent orange and blue can be different each time the system is powered up. Most Color Computer games start with a title screen and ask the user to press the reset button until the colors are correct. This is fixed on the Color Computer 3, and the other colorset can be chosen by holding F1 during reset. Lowercase and the 6847T1 The 6847 is capable of using an external character generator. Several third-party add-on boards allow the CoCo to display real lowercase characters. Late in the CoCo 2 production run, the enhanced 6847T1 VDG was used. It includes a lowercase character generator and the ability to display a green/orange or black border on the text screen. The lowercase capability is disabled by default on these CoCo 2s, and is not mentioned in the manual.