The VT01 famiclone can drive an STN-type LCD. According to the VT01 datasheet, the six bit color numbers have a different meaning in that case: rather than specify luma&saturation +phase, they specify four levels of red (bits 4 and 5), four levels of cyan (bits 2 and 3), and .... fours levels of something that the datasheet does not explain at all. The description of the STN-relevant chip pins is too cryptic to be intelligible.
A small number of ROMs exist that use color numbers formatted according to that specification. They are named "Portable FC-LCD 14-in-1 Game (Ch) [!]", "Portable FC-LCD 14-in-1 Study (Ch) [!]", "Portable FC-LCD S1 (SB01) Eng-Chi Dictionary 1 (Ch) [!]" and "Portable FC-LCD S2 Eng-Chi Dictionary 2 (Ch) [!]". I can make a palette that sort-of gets red and cyan right (first: normal NES palette, second: STN LCD palette):
Tennis2C02.png [ 2.45 KiB | Viewed 5066 times ]
TennisSTN.png [ 2.45 KiB | Viewed 5066 times ]
But the two extra bits are definitely used for something (first: Eng-Chi Dictionary screen using just the Red and Cyan bits, second: same screen using just the two unknown bits)
DictRC.png [ 1.33 KiB | Viewed 5066 times ]
DictExtra.png [ 268 Bytes | Viewed 5066 times ]
At least in the last image, these extra bits would either serve as a highlight or a shadow.
Now, I could just assume as these bits are for some sort of extra brightness, or "intensity", and make up some formula to use them based on what looks nice, but maybe somebody who has some experience with these types of displays has an idea. Unfortunately, I could not find a video or image showing how these particular displays look exactly; all videos I could find are of devices having TFT or similar displays that just show the normal 2C02 colors.
A small number of ROMs exist that use color numbers formatted according to that specification. They are named "Portable FC-LCD 14-in-1 Game (Ch) [!]", "Portable FC-LCD 14-in-1 Study (Ch) [!]", "Portable FC-LCD S1 (SB01) Eng-Chi Dictionary 1 (Ch) [!]" and "Portable FC-LCD S2 Eng-Chi Dictionary 2 (Ch) [!]". I can make a palette that sort-of gets red and cyan right (first: normal NES palette, second: STN LCD palette):
Attachment:
Tennis2C02.png [ 2.45 KiB | Viewed 5066 times ]
Attachment:
TennisSTN.png [ 2.45 KiB | Viewed 5066 times ]
But the two extra bits are definitely used for something (first: Eng-Chi Dictionary screen using just the Red and Cyan bits, second: same screen using just the two unknown bits)
Attachment:
DictRC.png [ 1.33 KiB | Viewed 5066 times ]
Attachment:
DictExtra.png [ 268 Bytes | Viewed 5066 times ]
Now, I could just assume as these bits are for some sort of extra brightness, or "intensity", and make up some formula to use them based on what looks nice, but maybe somebody who has some experience with these types of displays has an idea. Unfortunately, I could not find a video or image showing how these particular displays look exactly; all videos I could find are of devices having TFT or similar displays that just show the normal 2C02 colors.